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.

(Source: Anime News Network)

Note: During the original broadcast, the episode Hoka Hoka★Kanna to Futari Kiri, first included as an unaired special in the 6th DVD volume of HAPPY☆LESSON (TV), was also aired as the 9th episode of this season, with updated opening and ending to match the current season, as well as some minor changes to the episode itself.