Sentinel is a large, muscular man with a pot belly who has a full dark beard and scars around his face. He wears a leather hood with the straps securing it forming an X across the front of his face, a patterned tank top, shorts, and a fur cape. The leather overalls that he wears originally had the words "Bad Boy" written on the front on his stomach, which was later modified to have a Japanese character instead.
Despite being a coward and bully at heart, Sentinel somehow became the leader of a bandit gang and convinced them to adopt a policy of extorting goods from their victims and avoid killing them if possible. They do not accept bribes in return for safe passage, viewing this as an insult. The gang's unusual behavior is driven by Sentinel's aversion to killing, an unusual characteristic for a bandit leader. Depending on who he kills, he can get constipated for up to a week, and prefers to avoid it at all costs unless he has absolutely no choice.
In ES 590Sentinel's gang held up the caravan that Koyomi was traveling with. He tried to intimidate the merchants with the piston launcher and when Koyomi made her presence known, decided to focus on her to force the merchants into complying. Koyomi however reacted with indignation when the bandits attempted to steal the caravan's goods and challenged Sentinel into gambling for them. He fell prey to her superior skills and lost all of the loot back to her. Sentinel's pride would not let him back down and lose tremendous face, and he was put in the embarrassing position of having to wager the piston launcher. When Fury killed one of his men after he threatened Koyomi, Sentinel then tried to kill her in retaliation, but a well-aimed shot from Alita shattered his cleaver and scared the bandits into fleeing.