10-star DEX: Battle 2, Gunko Friend/Helper places Territory over enemy territory, then Carina uses her Super Switch effect for base ATK boost, then Nami's special to clear Paralysis. Lucci's crewmate ability deletes the Damage Reduction instantly.
Battle 3, Gunko eliminates enemy territory, while Coby, Lucci, and Shanks all remove Damage Cut. Coby removes the BLOCK slots, while Shanks sets the chain minimum to 2.75 to overpower the ATK reduction at 2.75 or less. Kuma support boosts type effects. Vivi support boosts slot effects without triggering an interupt. Don't switch captains with Coby's special, simply click CONFIRM without selecting someone to skip.
10-star STR: Battle 2, Gunko eliminates enemy territory. Shirahoshi uses Super Switch effect to lock slots, then Mansherry uses special for rainbow slots at 2.5x. You can't end up in Battle 3 as a QCK type without losing damage to a BLOCK slot on one of your characters, its better to just let Sh & Ma to be PSY, as they only get the Super Switch if starting as QCK. Use Carina to remove the Damage Cut, do not use her Super Switch effect.
Battle 3, Gunko reduces damage reduction to 5 and removes enemy territory. Hina removes DEF Up and will boost slot effects for Lv. 1 to 30. At Lv. 31+, she will give a base ATK boost instead due to the boss giving you a weak slot boost. Jinbe removes the last of the damage reduction and because of the 3 turns of damage reduction given by Mr. 3 and Ms. Goldenweek, he will further increase the ATK boost from Gunko, the slot boost/base ATK boost (pick whichever Hina set up), and the additive chain boost from Shirahoshi & Mansherry.
15-star DEX: I use Gunko as friend captain due to always having access to her. Uta is captain to avoid Special Reverse. Battle 1, use Uta's special, you will one round the boss easily.
Battle 2, use Uta's Super Class special to improve her effects for the final battle. Use Vivi's Super Switch effect for type effect boosts carried into the final battle. Use Rebecca's special, it's the only one you need, removing the DEF Up and giving you a type effect boost that will carry over to the next battle. Boa/Nami/Robin support on Coby guarantees a STR slot to break the STR slot barrier, and Coby will one-shot Battle 2.
Battle 3, Gunko special, Gunko special. Use Lucci's special to reduce Damage Cut, apply multiplicatice chain boost, and inflict Increase Damage Taken, then his VS effect for an additive chain boost. Use Coby to fully remove Damage Cut, and make Gunko your captain now that Uta has resisted all the Special Reverse for you.
15-star STR: You will not one round the boss. Battle 2, use Robin's Super Switch effect, then use Koala's special to remove the barrier. Your slot boost will carry over to the next battle, and the delayed type effect boost will not trigger an interrupt. The Whale Sharks, Helmeppo support, and Mr. 1 and Ms. Doublefinger support will remove all paralysis turns. The Special Use Limit will be reached but you can easily clear the battle now. Yes, Robin and Koala will be DEX but the benefits are worth it and you must start as INT. Just use them as the first tap as it does the least damage without the chain anyway.
Battle 3, Doffy adds to the chain. Use Gunko for the ATK boost. Then use King for matching slots on adjacent characters and to reduce the chain multiplier decrease. Use the other Gunko to regain the Super STR slot that King just turned into a regular STR slot. Do not use King first because he will set a weak ATK boost. Use Fujitora to eliminate decreased chain multiplier, do not switch captains. Normal switch Coby into Garp for a matching slot, then use Garp's special to eliminate Damage Cut and boost the final tap by 55% (stacks with switch). Don't use Fujitora's final tap, let Gunko do it for max damage. It's not worth starting with Garp for the Super Switch effect as you'll be stuck with the DEX typing.