Haruna Aizawa is forced to transfer out of the renowned K Academy after her politician father is involved in a corruption scandal. She thought that she had strong bonds with her previous friends, but they all too easily cut ties with her once the headline became public. As a result, Haruna holds a skeptical view of her new high school and future classmates. She believes that school life is like being on a monkey mountain, where monkeys in the same gang constantly fight and get back together again, and a hierarchy gets established. As such, she has no expectations of fitting into the pre-existing hierarchy at this school.

Masaru "Macharu" Yamashita is one of Haruna's new classmates, and even his appearance is akin to that of a baby monkey. He is remarkably sincere in his interactions with Haruna, and despite herself, she begins to open up to him. One day she makes the mistake of comparing their class to a pack of wild monkeys while in his presence, and he questions her about her standing in that situation. Is she looking on from the top? Or is she on the outside as an observer? Spending time with Macharu forces Haruna to confront her vulnerabilities and ponder why she is willing to let her guard down only for him—could this be love?