Koibito no Namae(1997)

One night, Ei Ariga runs into a very obnoxious playboy stranger. Then he finds out that the guy looks exactly like but otherwise is totally opposite to the timid and very polite Ryouichirou-san who lives alone in a very big apt and has hired his services (Ei-kun's father is a private detective), to find out why he doesn't remember doing some things and being at certain places. Ei-kun discovers that the nasty, violent and annoying carbon copy is called Naruaki and things get extremely complicated when he starts falling in love with both Ryouichirou and Naruaki...

Note: Includes the one-shot "Saikou no Kimi (最高の君)."