Kotetsu is the family cat in the story. He is a stray that Chie finds and decides to feed; after this initial encounter, he enters the family's izakaya and takes up residence with Chie and her father, Tetsu. His most recognizable physical feature is a mark on his forehead that resembles a moon. Despite being a pet, Kotetsu plays a significant role in the neighborhood dynamics. He is portrayed as a tough and capable fighter, a trait that becomes evident when he is pitted against Antonio, the prized cat of the local yakuza boss, Shachou. Kotetsu wins this fight decisively, an event that has repercussions for the human characters. He is also shown to have a sense of dignity and restraint. Later in the story, when Antonio's son, Antonio Jr., arrives seeking revenge, Kotetsu attempts to defuse the situation by showing respect for the deceased Antonio and refusing to fight, which ultimately prevents further conflict. His personality is characterized by a blend of independent, feral toughness and a quiet, loyal attachment to the Takemoto family, particularly Chie, who first took him in. His presence serves as a catalyst for several events in the plot, influencing the relationships between the human characters. His notable ability is his formidable fighting skill, which makes him a respected figure even among the animals in the neighborhood. There is also dedicated spin-off material focusing on his adventures titled "Doranko Kotetsu Funsenki," indicating his popularity as a character.