Yui Yamada has always been a shy girl, keeping to her small circle of friends and fulfilling her duties as the "Plant Appointee" by greenifying the school. Yet, one day, she ends up crossing paths with the track and field team's ace, Tomoka Kase. Kase is outgoing and athletic, while Yamada has never played sports or participated in a club. However, despite being polar opposites, the pair soon find themselves becoming closer. With lots to learn about relationships, and each other, will their feelings bloom into something more? [Written by MAL Rewrite]

Kase-san Series was originally serialized in Hirari, and moved to Flash Wings after the magazine was discontinued. After serialization of Yamada to Kase-san began, the first 5 volumes have been retroactively called "Koukousei-hen" (高校生篇, lit. "High School Student Arc") by the author and publisher. The series was published in English as the Kase-san and... series by Seven Seas Entertainment from February 28, 2017 to February 12, 2019.