簡易 Simple
場面はサニー号
The scene is Sunny (boat) ルフィとウソップがサメを釣って生簀へ Luffy and Ussop fish a shark and put it in the live container. (Fish tank type thing) そのサメが他の魚を食べちゃった This shark eats all the other fish.
チョッパーは医務室にいる
Chopper is in the infirmary.
ゴーストシップが近づいてくる
The Ghost Ship comes closer. その船に骸骨顔のアフロ頭が乗ってる On that boat an afro-haired, skeleton-faced person is riding. んで、いろいろ話してルフィが急に And then, they talk about a lot of things, and Luffy suddenly, 仲間にならないかと誘う ask him/her to join their nakama. (It's non-gender specific, but most likely a guy. p) オーッケーみたいな感じです It seemed like an okay.
名前はガイコツなんとかだった
The name was Gaikotsu-something. (Gaikotsu is skeleton).
(Original Poster) 俺の足りない脳での記憶はこれしか憶えられなかった
With my limited brain, this is all I can remember.
-->成り行きで仲間になる --> He ends up joining their nakama.