Yamada Seiji is a 22-year-old shonen manga artist with a tanned complexion, brown eyes, and neck-length gray hair. He initially mistakes fellow manga artist Sono Hanasaki for a woman, but upon realizing Sono is male, continues to develop romantic feelings for him. The two enter an intimate relationship. Yamada becomes distraught upon learning of Sono’s history of casual sexual relationships with multiple partners, leading to a temporary separation. He eventually reconciles with Sono after understanding the emotional trauma Sono endured from past abandonment and being used solely for sex.

Despite a ten-year age difference, Yamada often takes a proactive and initiating role in their relationship and intimate moments, making him the more active partner. His background reflects strong professional dedication to his craft, and his personal journey involves overcoming insecurities and accepting his partner’s complicated past.