Very interesting.
Shinji, the MC, is a mage that likes to take other men's women (netori). In addition to just being a good seducer, he says he uses weak hypnotic and aphrodisiac-like magics to enhance his seduction. The basic story is that he becomes the fourth member of a party called "Kakeru Ookami", consisting of three childhood friends: Arven (the guy), Milis, and Renka. Arven and Milis are dating, but Renka also seems to love Arven. Shinji's goal is to seduce both Milis and Renka, and alludes to having done similar seductions in previous parties.
From the way the story is told, I'm guessing this is a manga adaptation of a light novel series?