Imu has left many One Piece fans scratching their heads. Before, it seemed like either Fleet Admiral Sakazuki or one of the Emperors — probably Blackbeard — would be the series' endgame villain. Now, however, the shadow leader of the World Government is throwing their oversized crown in the ring. This mysterious figure knows much about the narrative's biggest secrets, including what happened in the Void Century. Unfortunately, they're playing their cards closer to their chest than most, so it's hard to tell who they are or what they want.
Source:https://www.cbr.com/one-piece-theory-imu-name-meaning/