In her third year in the workforce, just turned 20, Aya has her first junior colleague! His name is Yamato. He is 26 years old, six years older than Aya. Yamato-san is fresh and caring, and is very popular among the people in his department. However, for some reason, he teases and shows his "male" side only to Aya, who is in charge of training him....

The mature and smart Mr. Yamato takes the lead, and Aya is disturbed by his pace. She can't do her job at this point...! A secret office love affair with a slightly S-type older man...