The Professional Killers (jap. プロの殺し屋, pro no koroshiya) is a pack set on killing the monster, Kaibutsu. They were originally rained dogs who were used for guarding the top secret laboratory.; then one fateful day, Kaibutsu escaped from the lab. 16 dogs from the total of 50 guard dogs were chosen to track down the monster. The leader Jerome used to have 15 subordinates, but after four years only 4 remain. The others were killed and eaten by the monster. Kaibutsu also killed Tokimune, Gin's substitute, in the anime. When Weed and North were scaling inside of Gajō, the monster attacked North and killed him brutally (slashed across the body in the anime, decapitated in the manga). The others then counted on Smith to rescue Weed. When Smith sacrificed his life to save Weed (Ken and Kagetora were also involved as they went into the cave to help Weed in the manga). Then the other members of the Professional Killers risked their life trying to kill the monster. Afterwards; only Jerome survived the fight.