Rumi Natsumi is a first-year high school student by day and a lovely call girl from the Madonna agency at night. She is also a co-owner of the agency. One evening, the agency receives a call from Ryô Sugiura, a student from Mitaka, who says he has "problems" with his body when he masturbates. The manager calls Rumi to ask him to meet him. Once in front of Ryô, and after having enticed him in front of all the customers of the café where they met, she has the unpleasant surprise to see him turn into a horrible monster. Instead of running away, she decides instead to help him by teaching him to contain the monster that is in him, seeing this as a challenge.

Call me Tonight
Rumi's met a lot of guys through her job, and it's probably fair to assume that most of them could be said to have some sort of problem, but a man who literally turns into a beast when he gets turned on may be outside of this perky call girl's field of expertise. Still, a little challenge every now and again stimulates the mind and makes life so much more interesting, so she's willing to give it a shot.