Kotarō Tomoei is a third-year student at Kishimai High School and a central member of the Go-Home Club in the anime Caligula. He is a tall young man with slicked-back black hair and grey eyes, and he typically wears the school uniform with the blazer left open over a black floral-print shirt. His manner of speech can come across as rough or troublemaking, but this exterior masks a deeply caring and protective nature.

Kotarō is often described as the heart of the Go-Home Club, the person who holds the group together during times of tension. He is headstrong and can be stubborn, but he is motivated by a strong sense of duty toward his friends and school. He enjoys being relied upon and finds purpose in using his physical strength to help others. His future ambition is to become a lifeguard, reflecting his desire to protect and rescue people.

Within the story, Kotarō plays a key role in the group’s efforts to escape Mobius, the artificial utopia created by the virtual idol μ. He is a capable strategist and a natural leader, using his analytical mind to plan their actions. Despite his tough exterior, he shows genuine concern for the well-being of his fellow club members and is fiercely loyal. He forms particularly strong bonds with the protagonist Ritsu Shikishima and the other members, often acting as a stabilizing presence.

Kotarō’s development throughout the series involves confronting his own reasons for being trapped in Mobius and learning to rely on others as much as they rely on him. He matures from a solitary protector into someone who accepts and supports the group’s collective strength. His notable abilities include physical combat skills and a sharp intuition for reading people’s emotions and motivations, which make him an effective problem solver and mediator for the Go-Home Club.