Hitotose Chitose is now living together with his 5 teachers as his mothers when a mysterious girl appears and becomes their neighbor which turns out that that person is Nagatsuki Kuron who wants Mu-chan to be her mother so another sibling rivalry ensues as to who would end up as Mu-chan's child.



Note: During the original broadcast the episode HAPPY☆LESSON: Hoka Hoka★Kanna to Futari Kiri, first included as an unaired special in the HAPPY☆LESSON THE TV DVD Volume 6 on Dec 13, 2002, was also aired as the 9th episode of this season, with updated opening and ending to match the current season.

(Source: Anime News Network)