I. Guide for Clearing Captain's Coffers on Normal:
The biggest differences from Easy are that the monsters have increased attributes and that the boss' initial damage reduction has been increased to 60% from the original 40%. This is why I am recommending a special Cosmo:
Dealing true damage makes it possible to circumvent the boss' damage reduction.
You will need to battle Possessed Tokumaru Tatsumi + 4 monsters. Tokumaru starts the battle with an AoE attack and links himself to the four monsters with vines, thereby sharing damage with them. He will also revive 1 monster every 4 rounds.
The boss will transform once he drops below 50% HP. Upon transformation, the boss will use Soulbind on your Saint with the highest attack. This Saint will then share damage taken by Tokumaru, and if the Saint dies, Tokumaru's HP will return to the amount it was when he bound the Saint.
The boss will gain 60% damage reduction at the start of the fight, and this is reduced by 10% for every debuff it has. It is recommended to bring Seiya and Daidalos as they can both debuff the boss. You can also equip your attack Saints with Cosmo that can apply debuffs.
During the first few rounds, Daidalos keeps reducing the boss' attack power. Due to limited energy, Seiya will just be using basic attacks during this period. Once the boss transforms, stop debuffing it with Daidalos and instead weaken it with Seiya. Then rely on Golden Arrow Seiya coupled with Kingfisher to kill the boss with true damage. This makes it possible to circumvent the boss from healing itself with Soulbind.