Kenji Nakanishi is Mei Tachibana's classmate and Yamato Kurosawa's close friend at Toumei High School. The 17-year-old stands 172 cm tall, sporting distinctive messy light brown hair and chocolate brown eyes. Kenji possesses a perverted and impulsive streak, frequently engaging in inappropriate behavior like lifting Mei's skirt as a prank or openly ogling girls, particularly focusing on Asami Oikawa's ample bosom. Despite this, his nature remains well-meaning; he learns to recognize when he crosses boundaries and offers apologies. His actions often aim to amuse Yamato, though they sometimes cause unintended consequences, like unintentionally causing Mei to kick Yamato down a flight of stairs.

Kenji develops a significant crush on Asami Oikawa. Initially superficial and centered on her physique, his feelings evolve into genuine affection for her personality. Following Mei's advice, he confesses his honest feelings to Asami, leading to a happy and affectionate romantic relationship throughout the series. This relationship marks Kenji's key development, transitioning him from comedic perversion to demonstrating sincere commitment and emotional vulnerability.

Within the group, Kenji serves as comic relief but proves loyal to his friends. He leverages Yamato's popularity to interact with girls, yet remains observant of others' sincerity. Though initially disliking Mei, he befriends her, recognizing her positive influence—especially in navigating his relationship with Asami. His backstory reveals an interest in big breasts and a persistent desire to make Yamato laugh, consistent traits in his character. Kenji's surname, Nakanishi, derives from the kanji for "middle" (中) and "west" (西).