We never learn 21.

Nariyuki Yuiga comes from an impoverished family, so he’s eager to secure a full scholarship to college before he graduates high school. His principal agrees, with one stipulation—he must tutor three of the most talented girls at school and make sure they get into their target colleges!

Nariyuki has graduated from college and is now a newly employed teacher at…Ichinose Academy! Not only is he teaching at his alma mater, but he’s fallen for the teacher who’s taken him under her wing—Mafuyu Kirisu. And to complicate matters further, the two find themselves neighbors as well! What will happen in this heart-stopping final volume?!