One Piece: Becoming Sengoku's Son from the Start

After transmigrating into the world of One Piece as Donquixote Doflamingo's younger brother, Rosinante, he faces the prospect of being shot dead by Doflamingo three times in a few years.

Rosinante says there's no need to panic. After all, his godfather is Sengoku the Buddha, and he was born with a System...

Years later, Rosinante looks at the panicked Doflamingo. "Well, dressed in pink today, are we, my foolish brother? What do they call you again, that bird?"

This story is also known as "How I Brought My League of Legends Equipment System to the World of One Piece, Inherited My Godfather's Will, Became Fleet Admiral, Defeated the Pirates and World Government, and Shook the World!"

P.S. This is a Navy-focused story. The protagonist does not defect.