Sensei wa Bucchouzura shite Yattekuru

There's one man Yura despises at the day care his nephew attends: Mr. Kaji, the super cold and unfriendly day-care teacher. He's nice to the kids, but he doesn't even smile for the parents and guardians. To make things worse, Yura is traumatized from a past relationship, and Mr. Kaji sees right through him. But then, one day, this teacher Yura can't stand protects him when Yura's ex is being a complete jerk... by pretending to be his boyfriend...!!

(Source: Renta!)

Note: Includes a side story and an extra chapter.