Banetga-ui Jeotaek

A huge mansion in the city center. There, Cornell, the servant of the mansion where he lives with the Barnett brothers, is shocked by the fact that he starts to see the brothers he raised like his own children as men, and decides to leave the mansion on the brothers' 20th birthday. After a warm farewell and leaving behind regret, the moment he leaves, he loses consciousness and Cornell realizes that his body is different from before... "Now, the three of us will be together in this mansion forever."(Source: MrBlue, translated) Note: Includes 10 extra chapters.