Nagase Reika wa BSS in MM Este ~ Suki na Onna-tomodachi ga Eroi Massaji o Sareteru noni

A male protagonist harboring unrequited feelings for his well-endowed female friend, Nagase Reika, invites her to a couple's massage parlor equipped with a magic mirror room. As he secretly watches through the one-way glass, Reika receives an increasingly erotic massage from a male masseur named Katsuta that eventually escalates into full sexual intercourse. Meanwhile, the protagonist is attended to by a female masseuse who teases his voyeuristic desires and gives him a handjob while he watches. Fueled by his current situation and memories of a past experience, he ejaculates as he watches Reika and Katsuta. The story concludes with the pair leaving the parlor, Reika having thoroughly enjoyed herself while the protagonist is left grappling with mixed feelings of arousal and cuckoldry.