Kei Inui

Kei Inui or Cerberus is one of the characters featured in Succubus Heroines Eroge.

Pre-Transformation
A classmate of the main character.

Even though she's a first year student, she's the ace of the track and field club. Even though she's a girl she has a rough, crude personality, and she uses coarse language. That's why her classmates treat her as a tomboy. She's incredible at sports, but fails hard when it comes to other things like studying or cooking.

The way she interacts with the main character, it's almost like she's another guy friend. They get into fights sometimes too. But even still, she loves animals and cute things.

It seems that she's really worried about being seen as manly.

Cerberus
Kei, after having been transformed into a succubus by Asuna.

The high energy she used to use for running is now entirely used for sex. Perhaps as a backlash because of her complex, she's obsessed with her own femininity. She uses all sorts of means to try and assert it to the main character.

She is extremely sensitive to the odors of men, and especially that of the main character. She attacks like a beast hunting, and tries to fuck like an animal. She appears to be almost like a bitch in heat.

Trivia

 * Although her succubi form, Cerberus, look like Werewolf, the "ears" are actually horns, while the large claws are actually deformed wings.