R-15 is about a boy, Taketo Akutagawa, who attends a school for geniuses: Inspiration Academy Private High School. Taketo is a genius novelist and writes erotica. Despite negative perceptions many people have of him, he aims to be at the top of his class and be recognized as the world's greatest writer. (Source: Wikipedia)

As the fall season nears its end, Chidori Yoshino, a member of Strega, abducts Junpei Iori. Meanwhile, Makoto Yuuki and the Specialized Extracurricular Execution Squad (SEES) annihilate the Arcana Hanged Man. Soon after, a mysterious playboy named Ryouji Mochizuki transfers into Gekkoukan High School's Class 2-F. Supposedly having achieved their goal, the members of SEES believe they are free from the battle that has ruthlessly stolen away the lives of their loved ones. And yet, Tartarus and the Dark Hour continue to exist, undeterred by the extermination of the twelfth Shadow. Distraught by their apparent failure, SEES must cope with their personal struggles and discover whose sake they fight for. As Makoto and Junpei's journeys of self-discovery progress, Ryouji's identity and the reason behind Aegis's hate for him become clear.

Due to childhood circumstances, first-year high school student Saki Miyanaga hates anything related to mahjong. When she does play the game, she keeps a low profile to avoid standing out. One day, her friend Kyoutarou Suga drags her along to the school's mahjong club. There, she meets Nodoka Haramura, the champion of the previous year's national middle school mahjong championship, and Yuuki Kataoka, a fellow club member. As the club play a few rounds, Saki attempts to hide her talent. However, the club president, Hisa Takei, notices Saki's unusual playstyle. Realizing her potential, she puts Saki's real ability to the test—proving her to be more talented than expected. This revelation damages Nodoka's pride, and their relationship gets off to a rocky start. Saki ends up joining the club, and after clearing up the misunderstandings between her and Nodoka, friendship blooms between them. As Saki slowly warms up to mahjong once again, she and the rest of her club only have one goal—to win nationals!

Video games, especially puzzle games, were always at the center of Konomi Kasahara's life. However, upon entering Hanamiya High School, she decides to break away from this lifestyle. As Konomi wanders the halls in search of a new activity to engage herself in, she stumbles upon a gigantic wall owned by the school's rock climbing team. Fascinated, she attempts to scale the wall, discovering that she can use her puzzle-solving skills to help her reach the top. Certain that she has found her calling, Konomi immediately joins the club. As she strives to improve her climbing skills, Konomi, alongside the rest of the Hanamiya Climbing Team, will learn what it truly means to be a sports climber and work to achieve victory in the upcoming competitions.