Riki Naoe is a high school student temporarily residing in the female dormitory while his male dorm undergoes renovations. He shares a room with Kudryavka Noumi, his close friend with whom he shares a romantic relationship. They actively conceal this cohabitation arrangement due to dormitory rules prohibiting male and female students living together. During this summer vacation, most other members of their friend group, the Little Busters, have departed, leaving Riki and Kudryavka largely alone.

Riki possesses a slim build, standing 166 cm tall and weighing 54 kg, with brown hair and hazel eyes. Orphaned in childhood, he developed narcolepsy, experiencing sudden, uncontrollable sleep episodes. Despite these challenges, he displays straightforwardness, kindness, reliability, and strong common sense compared to peers, making him a dependable figure who supports others through difficulties.

Within the narrative, Riki interacts with specific characters. He assists young Shiina Arizuki in her goal to win a water rocket competition, aiding her material search and supporting her astronaut aspirations against her family's wishes. He encounters Yuuki Himuro, a science club president conducting experiments who previously roomed with Kudryavka. Kanata Futaki, the girls' dormitory head and a returning character, expresses concern over Riki and Kudryavka's relationship while enforcing rules. Other interactions include the former dorm head "A-chan" and Shiina's older sister, Ui Arizuki.

Riki adopts a protective role toward Kudryavka throughout their cohabitation, navigating the challenges of secrecy and Kudryavka's personal struggles. This period deepens their romantic involvement, and they eventually have a daughter named Kaya Naoe. His responsibilities grow when he becomes president of the Rocket Club, aligning with his support for Shiina's water rocket endeavors.