Uchi No Ko Ni Narinasaiうちのこになりなさい; Become My Lover; Uchinoko ni Narinasai

From Bliss: While buying food at the supermarket, Sunao Morihara gets kidnapped by a strange man, Kuon Tachibana, who turns out to be incredibly rich! His motive? He wants Sunao to be his friend. However, before Sunao realizes, being Kuon's "friend" actually means becoming his wife!