Ace

A or Ace (エース,) was one of the Port Mafia's Executive members.

Personality
Though he is an Executive, he has no loyalty towards Port Mafia and tried to recruit Fyodor in his attempt to rebel against Mori Ougai. He is shown to be a very cocky person.

Ability
Ace's ability, The Madness of the Jewel King (宝石王の乱心,), is an ability that turns his subordinates' life (those who equip the collar he gave) into jewels which worth according to the target's lifespan.

Background
According to Chapter 42, Ace gained his position as an Executive by paying Port Mafia a large sum of money. It is shown that Mori and Kouyou both conscious of his true self that they put no trust to Ace but Mori allows him to be in charge of Fyodor's interrogation.

Originally, he was a gambler who laid waste to Port Mafia's casino before he joined Port Mafia.