Inga no Sakana

Cousins and childhood friends, Issei and Ryouichi. Between bossy heir of a company president Issei and gloomy, always obedient Ryouichi arose a warped master-slave relationship. Letting the adored Issei conquer him, young Ryouichi gave his body over to pleasure. However, a few years later, with these two working at the same company, has the relationship between these two started to change?

(Source: Shodensha, translated)