Who is the Japanese voice actor for Buchi?

The Japanese voice actor for Buchi is Yasuhiro Takato.

What role does Buchi have in that anime?

In One Piece, Buchi is listed as a supporting character.

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Buchi

ブチ

About

Buchi (ブチ, Buchi, romanized as "Butchie" in the English versions) along with his fellow pirate Sham, are the two lookouts of the Black Cat pirates. They are also known as the Nyaban Brothers (ニャーバンブラザーズ, Nyaaban Burazaazu). (Source: Wikia)