The original guide was written by GameFAQs user Klikster for PS4 version of One Piece: Pirate Warriors 3. I only copied the text from his guide to Steam and corrected some differences (it's seems that PC and PS4 versions have some of them). I hope that reading that info at Steam will be more comfortable than browsing at GameFAQs.

The link to original guide: http://www.gamefaqs.com/ps4/834698-one-piece-pirate-warriors-3/faqs/72328?page=0#Legends Log
Also, Klikster's guide was a result of several guides / pieces of information:
Twinfinite's Treasure Events Guide - http://www.twinfinite.net/2015/08/25/one-piece-pirate-warriors-3-guide-how-to-trigger-all-treasure-events/
Arlong Park Forums: Mr Luffy's Guide - http://apforums.net/showthread.php?t=41669&s=779dbeedc1b79b2724edc49af8d30c2a&p=3440839&viewfull=1#post3440839

P.S.: Sorry for my English, it's not my native language =)

P.P.S.: Guide is still in progress.

One Piece: Pirate Warriors 3 contains Treasure Events which are hidden sequences that only play out when certain criteria are met by the player. These range from completing certain actions quickly, to beating levels with specific characters. While none of the Treasure Events in One Piece: Pirate Warriors are especially difficult, some will require a bit of a time commitment since they require specific characters that most players don't really use often, or are unlocked later in the game.

Characters you will want to focus on leveling up to make your life easier are Zoro, Sanji, Brook, Nami, Ivankov, Buggy, Jimbei, and Boa Hancock. You'll only need them to be powerful enough for the One Piece: Pirate Warriors 3 Treasure Events that require them, so don't stress yourself out trying to max out every single one (unless you want to, of course).

1. Defeat all Marine Captains approaching Nami. If she falls, you'll have to start over.
2. Destroy every single Captain Morgan Statue.

1. You must play as Zoro. Clear the first two cannon rooms while taking as little damage as possible.
2. Play as Luffy. Defeat Alvida (she will appear twice). It must be you who defeats her, not one of your allies. Now get Captain Buggy to about 40% health and the event will trigger.

1. Prevent enemies from destroying Usopp's barriers while also clearing enemy controlled territories. As long as you keep an eye out on what's going on around Usopp, you should be fine.
2. When Kuro first appears, lead him to Usopp. This means you must bring him to where Usopp set up the barriers since he won't leave that small area. Once Kuro gets close enough, the Treasure Event will trigger and you can defeat him.
Note: Kuro will go straight to Usopp if you won't help Nami protect treasure on board of the ship.

1. There will be a group of Pirate Captains with “?” icons. Defeat all of them.
2. Locate and defeat Dracule Mihawk.
3. Complete Sanji's Strategy. This means NOT trapping yourself in the territory directly west of where Krieg first appears. If you clear it fast enough and exit through the south, an event with Sanji will trigger. The territory will have a (?).

1. You must play as Sanji. There will be a group of Fishman Captains with “?” icons. Defeat them all.
2. When the marines land, protect all ally fighters captains on the coast. Achieved by targeting the marine captains.
3. Play as Zoro and defeat Hatchi (the octopus dude) before the boss battle against Arlong.
4. If you did everything correct and none of your allies were defeated, a “?” mark will appear over Arlong when you initiate the battle, meaning it's Treasure Event time.

1. You must play as Zoro and defeat Tashigi.
2. Play as Luffy and battle Alvida in the southern part of the map.
3. There will be three lighting rods that you will easily find since they appears as “!” on the map. Destroy them quickly. The Treasure Event will trigger once Buggy arrives.

1. You must play as Luffy. Immediately head over to Wapol (clearing territories on the way) as soon as he appears. Defeat him.
2. Protect all Lapan from retreat. After you defeat the first Lapan, allies will appear on the map. Protect them all until the scene activates.

1. Smoker will appear in the southern section of the map. Find and defeat him.
2. Robin will appear for a short period of time in the northeast. Hurry to her and defeat her in combat.
3. You must play as Zoro and meet up with Mr. 1.
4. Playing as Sanji, meet up with Mr. 2. This is a bit tricky because you must defeat Tashigi beforehand. In order to get Sanji to defeat Tashigi (as he can't personally harm a female leader), you must attack with your support characters.

1. Marine Captains will appear with a “?” icon. Find and defeat them.
2. Blackbeard and Burgess will appear. You must defeat Blackbeard first or else he will flee and you will have to start over.

1. Quickly defeat the Captains trying to attack Nami and Nico Robin. Make sure that neither of your allies retreat.
2. Afterwards, defeat all Captains trying to attack the Going Merry. Eneru will first appear in a red zone to fight you. Upon defeating him the 2 captains with the '?' should appear. Some have found it helpful to not defeat Enel too fast or first lure him away.
3. Eneru will appear in another red zone. Quickly take over that territory and defeat him before he appears for the final time as the stage's boss in the northern part of the map.

1. You must play as Sanji and defeat all of the enemy Captains that appear. They will once again have the “?” icon, so they'll be easy to pick out of a crowd.
2. Win against Franky. He will appear a second time in the southwest of the map. This time, he should have a “?” icon, defeat him again.
3. There will be 10 enemy waves in front of the mansion. Defeat all of them before Nami breaks in.

1. Play as Zoro and face Kaku.
2. Play as Sanji and face Jyabura.
3. Reach the pillars of Bridge of Hesitation before Lucci. A difficult one. The easiest and probably only way is to complete the task from legend diary (see "Legend Diary" - "Chapter 3" - "Enies Lobby"). If you did everything right you will be there just a few seconds before Lucci, there will be "?" mark during the fight with him and the event will trigger a little bit later.

1. There will be a group of Captains with the “?” icon. Defeat them as fast as possible.
2. Defeat Aokiji when he apperas to the south. Possibly the hardest boss in the game in relation to your current level. Will most likely not succeed your first try (between lvl 20-30). But if you must ASAP, max your support characters early whittle his health to arround half and use all your support allies' Kizuna Rush mode back-to back. Be wary that if Aokiji freezes you, Kizuna Rush mode is instantly cancelled at the support is back to level 1. Also if you take too long, Garp will capture your territory, resulting in a Game Over. Might be a good idea to save beforehand.

1. You must play as Brook and let no captains retreat while you locate and defeat Doppleman.
2. Play as Brook. Continue until you defeat Doppleman and open the doors to the new area. Here, you must defeat every enemy in the graveyard before facing Perona, and I mean every enemy aside from those within Perona's territory and the shielded enemies. Even then you must make sure you run into every Strawhat and make sure they are done fighting/moving unless they entered Perona's territory. Also make sure as many of the Strawhats talk to you as possible beforehand. Only then should you face Perona and trigger the Perona dialogue scene. After that clear the lower and upper platforms of all general zombies and then trigger the Oars cutscene. Then just play as normal until the 2nd Oars encounter just before the bridge is built. A question mark appearing on Oars is a good indication you may be on the right track.
Note: Ok, I think this is the most difficult in the game. The description above is not fully right. I triggered this event as Brook. I gathered all the team before fighting with Perona (there must be all of them except Nami, also there is a counter of nakamas rested, in bottom right corner, under the text with current mission). Then I beated Perona but eventually missed 2 zombie captains. I dunno why but the treasure event worked fine after that - just beated Oars twice while were protecting the sappers. Made it with 47 lvl. Brook on easy difficulty.
3. Defeat Kuma once he appears.
4. When you KO Oars in the upper platformed area the first time, Moria will appear + 3 Dopplemen. Moria appears in the area with Nami, defeat him (and possibly one other Doppleman) to get the scene.

1. You must play as Nami and defeat all of the Marine Captains. They will have the “?” icons, as usual.
2. Kizaru and Sentamarou will appear in different areas of the map. Immediately head towards Sentamarou and defeat him before Kizaru makes it to him.
Note: It's seems that the event will trigger even if you beat Kizaru first.
3. Afterwards, two Pacifistas (Kuma cyborgs) will appear. Lure them to the south central area of the map. This is where Trafalgar Law is located and he is need to trigger the treasure event. Simply get both cyborgs into the room and defeat them.

1. Play as Ivankov then help Crocodile win against the Monotaurus.
2. Buggy will join shortly afterwards, at which point you will need to head to the southwest quickly in order to free Mr. 1. Crocodile will be your support up to this point in order to get into the southwest.
3. Free all prisoners. Not sure Mr 1 counts, but there are 3 aged areas to the northeast with (?) icons. Buggy eventually opens all of these if you clear the areas fast enough and don't let Minotaurus harass him or get him to retreat.
4. Clear the First Control Room before Mr 2 (disguised as Megellan) reaches Second Control Room. You need Crocodile to open the doorway to the corridor leading to this area before Mr 2 opens it.

1. Play as Ivankov and make sure not to capture Smoker's territory. Instead, locate and defeat Kuma.
2. Now you must play as Luffy in order to attract Boa Hancock. Start a fight with Smoker then run away and try to talk to Boa Hancock. Go back and continue your fight with smoker in order to trigger the scene that brings Boa Hancock into the fight.
3. Play as Buggy and face Dracule Mihawk.
4. Play as Jimbei and defeat Gecko Moria. This all will earn you the Treasure Event.

1. You must play as Hancock and defeat Sentamarou before fighting Garp.
2. Doflamingo must be defeated while Crocodile is nearby. If he isn't, then lead Doflamingo towards him.
3. There will be Marine groups with the “?” icon. Defeat all of them before they can takeover Whitebeard's territory.
4. Quickly run to the scaffolding and clear it. You have to be very fast. You'll know you got it in time because the “?” icon will appear over Garp.
5. Once Ace is freed, you will have to deal with more Marine Captains that have the “?” icon.
6. Playing as anyone other than Luffy or Whitebeard, defeat Sentamarou when he retreats to his Pacifistas. He must be defeated before they are.

1. When Nami first appears, allow her to meet Usopp before Sanji gets near Nami. If Sanji turns to stone upon witnessing Nami(-chwaan) you will fail. If successful, Sanji will divert his attentions to Robin, who will turn him to stone no matter what.
2. During the mission Boa Hancock will retreat to her ship, escort her in order to receive a cutscene when she arrives safely.
3. At the end of the level, Sentamarou will appear with four Pacifistas. Defeat all of the Pacifistas before delivering the finishing blow to Sentamarou. Be ready to dodge a lot since Pacifistas are no joke when it comes to battle, and four of them can prove to be quite difficult.

1,2,4,5. There will be four territories with the “?” icon, clear each of them.
3. While clearing the territories make sure no allies retreat before you reach Hody.
6. You will fight Hody and he will retreat before appearing in the northeast section of the map. There will be two switches that you must destroy, and they will be marked on the map with a “!” icon. Destroy both as quickly as possible then head over to Hody to trigger the Treasure Event.

1. Free Sanji from the Southern portion of the map in order to allow him to make his way to Vergo and fight him.
2. Playing as Zoro, engage Monet.
3. Prevent any marine captains from being sealed off in the first Shinokuni contaminated zone. Be advised that when you exit the contaminated zone, the zone will be sealed off instantly, regardless of the timer so try to be the last one out.
4. When leaving the zone, enter the central area where you will encounter marines being locked into small quarters. Free all 4 of them with visible (?) icons by defeating the enemy captains in front of each door.
5. After freeing the captains, head on over to Law and Smoker and make your way to Vergo (he'll be in the SAD lab). Fight Vergo with Smoker close by to trigger one of the Treasure Events.
6. After some time, most of the level will be contaminated leaving only the northwest section of the map. After about a minute, Caesar Clown will appear and he must be defeated as quickly as possible. If your friends clear one of the enemy territories before you beat Caesar, you will fail to unlock the Treasure Event. (If a scene with Law plays out beforehand (indicated by a [...] prompt) you have failed, even if you defeat Caesar Clown immediately after.)
7. Playing as Luffy, make sure that no allies retreat as you fight and wait for the final fight against Caesar Clown. If done correctly, the Treasure Event will play right before the confrontation.

1. Rush over to the Green Bit section of the map (located in the northwest) and clear it out. You want to race ahead of both Law and your other allies because once Law reaches the location, Bellamy will appear. Quickly defeat Bellamy before he retreats.
2. There will be Pirate Captains after the Flame-Flame Fruit in the Colosseum. Once again, race ahead of Law to reach the area and defeat the captains. If Law gets there before you, there is a very high chance that he will die.
3. Now you just have to locate Blackbeard and defeat him as fast as you can. He is a challenging fight, so make sure that whoever you use is at a relatively high level. Put your Kizuna Rush to use and you should be fine.

Okay, might as well do the other 8 objectives for 100% though really it just boils down to 1 unique one. For EVERY stage (Except some of them) the first 8 are the following:

1. Complete the Stage
2. Achieve S ranking for KOs
3. Achieve S ranking for (!) points delivered (support attacks)
4. Achieve S ranking for a low enough completion time
5. Achieve a comprehensive S Ranking in a single playthrough
6. Complete all Treasure Missions
7. Beat in Hard Mode (or Super Hard Mode).
8. Defeat the final boss with a Kizuna Rush finisher.
The 9th one is where things get a little more interesting as it's a wild card objective unique for each mission. ShonenGameZ.com did a good job translating the in-game description of these, but they can sometimes be vague as I found out. Most are pretty self-explanitory. Note that the 8th and 9th are sometimes flipped

Gain 500+ (!) in a single battle. Effortlessly done when going for an S ranking.

Clear the stage with no allies (Villagers) retreating. Self-explanatory

Clear the stage with no allies (Villagers) retreating. Again, self-explanatory

Defeat Mihawk. Treasure mission already makes this manditory

Clear the stage with no allies (Villagers) retreating. Again, self-explanatory

Defeat Tashigi in a Kizuna Rush finisher. Unique because she's the only non-final boss enemy in the game that requires this

Clear the stage with no allies (Villagers) retreating. Again, self-explanatory

Defeat Crocodile twice. Missable if you spend too much time in the lower territories trying to get an S ranking. He first appears in the central territory beyond Mr 1 and Mr 2.

Gain 1500 KOs (!). Again, effortless when going for an S ranking

Quickly defeat Wiper. Easy to get without trying.

1. Complete the episode as Luffy.
2. You must kill 3 messengers before they will reach red zones. You will see all of them as big red spots, just after the beggining of Front Gate fight. They will run to the red zones only if the will see Nami, so you can just go with her or even move along and beat them beforehead.

All Strawhat strategies succeed. When you cross the bridge and get Franky, go to Jyabura's territory and clear it & defeat him. Then head further to the corridor leading to Lucci and destroy the switch. This will block Spandam temporarily. From then on, capture territories in a counter-clockwise fashion until they are all captured, saving Kaku's for last. Only then proceed to Lucci. This way, Sanji get's the Jyabura area, Sogeking gets the bridge, Franky get's the pantry and Zoro gets the garden. Strategy successful. Then just beat Lucci, save Robin and escape ASAP.

1. Do not let the pirate with Franky's pants retreat. Easily done going for S or even just your first time through
2. Defeat Coby twice. Not difficult. Just remember to get him the 2nd time in the SW corner of the map and not just go straight for Garp/Aokiji at the end.

Yet again, don't allow any retreats in the stage.

Clear stage with Law maintaining a certain amount of life. I dunno certain amount needed but I think that it must be something like 75-80% because 50% and more certainly is not enough. Also try to protect Law and finish final battle with Kizaru ASAP.

Defeat Minotaurus 4 times. Easy to miss if you don't keep an eye on him, as the stage tends to reach the boss event by the time it's necessary to put him down the 3rd time.

Defeat all bosses. Important to note you cannot complete this with Luffy because Hancock refuses to fight you. Also, it's important to go for Hancock & Kuma before defeating Smoker because there'sa good chance the next phase of the stage will start and they will retreat. Also, be sure not to accidentally activate the final boss event at the end.

Defeat all bosses. Important to note you cannot do this with Luffy or Whitebeard because you cannot take part in the final phases of the stage, namely fighting dual-fruit Blackbeard. Early on save Garp and Kizaru for last. Also be sure to defeat Sentamarou when possible because he tends to stay at the sidelines minding his business. Challenging because most of the characters at your disposal will likely be under-levelled (though can be fixed with beli) and likely unfamiliar to play as.

Do not allow Perona or Hancock to retreat. Not difficult at all.

Escape from Ryugu Palace. Sounds easy, but the trick is to know which characters allow this. You can only do this with Zoro, Usopp or Brook. They will begin locked in a room until Brook uses his soul powers to scare an enemy into opening the gate.

The last one that requires no retreating allies. This includes not allowing any marine captains to be abandoned in the Shinokuni contaminated areas.

All strawhat strategies are successful. This one is rather vague but not too hard to figure out. The most difficult portion is early on. Your goal is to get Ceasar Clown to the drop point, but also prevent Bellamy's group from taking advantage while your're gone. So take care of the mission-based captains in the town, all the while spending a bit of time supporting Law. All 4 captains in town must be defeated before Bellamy appears, and he must be defeated before he retreats. If you succeed, you will get a green "objective success" message jsut before Doflamingo appears. If not, you will get a red "objective failed" message instead.

A few other actions that may affect this Dressrosa mission:

- Going into the collosseum with Law
- Preventing all allies from retreating (against their will). This includes Bellamy who appears aftter - Fujitora & Doflamingo appear on Green Bit
- Preventing the Blackbeard captains from taking the territory to the south
- When Kuzan becomes a support, use him to destroy all underground entranceways (they look like phone booths) marked with a (!).
- Help conquer the Smile Factory before beating Fujitora and Kizaru
- Conquer the Territory where Fujitora starts
- Conquer the Territory where Burgess starts
- Conquer the Territory where Blackbeard starts
- When Bellamy returns as an ally, make sure he doesn't get defeated early on
- When facing Doflamingo (final boss), make sure to deliver the finishing blow on the real Mingo, not the puppets.

Note: I did almost everything of that and it worked fine. I believe that you must follow the instruction and complete all the tasks that will appear in bottom right corner. Don't forget to capture Toy Factory before Colosseum and to destroy all the phone booths with Kuzan. Remember - saves are your friends.

Blueno Coin: This unlocks gear 2nd. Acquired once Water 7 is completed with Luffy
Rob Lucci Coin: This unlocks Gear 3rd and TS Luffy's Elaphant Gatling. Acquired upon completing Enies Lobby with Luffy.

Kaku Coin: This unlocks Asura and TS Zoro's 2nd Special. Acquired upon completing Enies Lobby with Zoro
Sword #1 Coin: This is a costume unlock. Acquired upon completing Loguetown with Zoro
Sword #2 Coin: Another costume unlock. Acquired upon completing Thriller Bark with Zoro.

Enhanced Clima-tact Coin: Appears to be a costume unlock. Acquired upon completing Skypeia with Nami. Free Log completion required.

Jyabura Coin: Gives PTS Sanji his Diable Jamble ability and TS Sanji's Hell Memories abilities. Acquired upon the completion of Enies Lobby with Sanji.

Kabuto Coin: Necessary to gain Usopp's 2nd Special (both PTS & TS). Acquired upon completing Skypiea with Usopp.
Sogeking Coin: Necessary to gain a unique costume unlock. Acquired upon completing Enies Lobby with Usopp: Free Log completion required

Rumble Ball Coin: Necessary to gain the Monster Chopper special for PTS Chopper and TS Chopper's 2nd special. Acquired upon completing Enies Lobby with Chopper.

Franky Coin (no association with Franky's limit breaking coin): Necessary to gain PTS Robin's "Grab" special & TS Robin's 2nd Special. Acquired upon completing Water 7 Departure with Robin.

Edit: Looks like Law and Tashigi get a gold coin each for completing Punk Hazard with those characters. For both, it goes toward their 2nd special.