After a scandal involving her father forces her to leave a prestigious academy, Haruna Aizawa enters a new high school with a cynical attitude towards her peers. She likens the dynamics of school life to monkeys on a mountain, constantly fighting and reconciling. Masaru 'Macharu' Yamashita, a classmate resembling a baby monkey, approaches Haruna with genuine sincerity, gradually breaking down her defenses. As their bond deepens, Haruna is prompted to reflect on her feelings, wondering if her willingness to be vulnerable with Macharu signifies something more profound than friendship.