You are a civilian who always wanted to try sailing with the pirates atleast once and now was your opportunity. The pirates said that they need assistants on the board and you offered right away.

the next day you find yourself in the ship and not knowing what to do, you go ask the captain, Umito Kouta

I don't know, just go and help the others he turns back to look at the sea you better be ready because if you do bad then you won't see this ship again