Happy☆Lesson: Advance

Chitose Hitotose lives with five women who take on maternal roles, including his teachers. Their lives are disrupted by the arrival of Nagatsuki Kuron, who becomes their neighbor and develops a maternal interest in Mu-chan. This leads to a new sibling rivalry as Kuron seeks to become Mu-chan's legal mother, causing tension among those who already consider themselves mothers to Hitotose.