After being rejected by Shirahoshi, he shaves the top of his head in depression.He also has sharp teeth, with bigger webs between his fingers than most fishmen, a very thin, pointy nose and a prominent hunch that puts his head on equal level with his shoulders.
Unlike most cruel pirate captains who dominate over their subordinates, Decken has a casual relationship with his crew. When Noah collides with the bubble surrounding Fishman Island, Wadatsumi falls off the ship and Decken ignores his pleas for help and calls him a sacrifice.
He is attracted to the Mermaid Princess, sending her letters, packages, and even threatening marriage proposals.
Decken formed an alliance with Hody Jones, with the understanding that they are equals, not leader or subordinates.
However, Decken has no interest in the goals of the New Fishman Pirates and only used this alliance to get closer to Shirahoshi.
His obsession led to him reserving his right hand for Shirahoshi alone, targeting her since she was only six years old, and going as far as to write wedding invitations before even proposing to her.