Mitsugu Kurokawa is a Japanese salaryman with black hair, black eyes, and a height of 176 cm. He first met Tomoe Tatsumi in Tokyo when Tomoe traveled there for a university entrance exam. Kurokawa was drinking with his friend Taichirou Isogai when Isogai vomited on Tomoe's coat. Kurokawa assisted Tomoe by cleaning the coat and offering temporary shelter after the hotel address became unreadable due to the incident. This encounter sparked romantic feelings in Kurokawa, culminating in a kiss when Tomoe departed for Nagoya.

After Tomoe passed the exam, Kurokawa offered lodging in his Tokyo apartment, bringing them closer. He later confessed his love, beginning a relationship opposed by Tomoe's older brother, Souichi Tatsumi, due to Souichi's homophobia rooted in past trauma. Despite Souichi's attempts to separate them, Kurokawa and Tomoe stayed committed.

Seeking opportunity for Tomoe's career, Kurokawa and Tomoe moved to California. They married there after learning of the state's legalization of same-sex marriage—news delivered via a disapproving phone call from Souichi. This marriage formalized their partnership, though Kurokawa maintained a fearful attitude towards Souichi's frequent threats. Their eventual return to Japan caused logistical disruptions for family and friends.

Kurokawa's personality combines affection and attentiveness toward Tomoe with apprehension regarding Souichi's volatility.