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Tenma's Younger Sister and Harima's Manga Assistant
Yakumo is Tenma's younger sister and a first-year high school student with a strong love for her older sister. A multi-talented young woman, this soft-spoken girl is a far better cook than Tenma and has earned the affections of many boys in her class, including second year class rep Haruki Hanai. To Yakumo's dismay, Hanai would follow her to every club that she was invited to join which kept her from considering taking interest. But when Akira bans Hanai from joining the Tea Club, Yakumo joins it. Yakumo has the ability to sense the thoughts of those with strong feelings for her which allows her to know whenever Hanai or any other lovelorn boy is nearby. She also has an interest in animals as shown through her care for pet cat Iori and is always a welcome addition with her older sister's circle of friends.
Upon meeting Harima, Yakumo is surprised by the fact that she can't sense Harima's thoughts since the guy is madly in love with Tenma. This, combined with Harima's large number of animal friends, draws Yakumo to the guy as she wants to talk about animals with him. She becomes Harima's closest friend to the point where Harima would normally address her as "Imouto-san" and where he trusts her in assisting with his manga and keeping work on it secret. However, their bond leads others within school to misunderstand the relationship as a romantic one and leads Yakumo in a brief rivalry with Eri, who has her own romantic interest in Harima.