Nijuu to Seijuu

In her third year as a working adult, Aya, who has just turned 20 years old, has her first kohai! His name is Yamato Higa-san (age 26). Higa-san is kind and pleasant to be around, so naturally he is very popular with everyone in the department. However, for some reason, he teases only Aya, his trainer, and shows her his alpha male side... With mature, smart Higa-san taking the initiative at every turn, Aya cannot focus on her work…!

(Source: K MANGA)