Saruyama!

After her politician father is disgraced in scandal, Haruna Aizawa transfers to a new school. Haruna is convinced that school life is just like a monkey mountain—all the monkeys form cliques, get into fights, and get back together again. She even meets a boy named Masaru (aka Macharu) who reminds her of a baby monkey!

(Source: Viz Media)

Includes a side-story about Masaru's younger sister in volume two, a side-story about Atsu and Macharu's meeting in third grade in volume five, and a side-story taking place after graduation in volume eight.