S1E32 — Witch of Cocoyashi Village! Arlong's Female Leader!
One Piece — Season 1, Episode 32.
Zoro is captured by the fishmen after Usopp and Johnny ditch him, and it's revealed that Nami was part of Arlong's crew the entire time. When a group of Fishmen attack Cocoyashi Village, Usopp comes to the rescue.
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