Nijuu to Seijuu

In her third year in the workforce, Aya, who has just turned 20, finds herself with her first junior colleague! His name is Yamato. He is 26 years old, six years her senior. Yamato has a refreshing and caring demeanor, making him well-liked by the other members of the department. However, he enjoys teasing Aya quite a bit and occasionally gives her a hard time, even though she is supposed to be the one training him… Whenever Yamato's intelligent and mature side comes through, Aya becomes flustered. At this rate, she won't be able to focus on work...! A secret office romance with a slightly sadistic younger colleague… (Source: Bessatsu Friend, translated) Official Web Comic