Asuna Yumemiya

Asuna Yumemiya or Astaroth is one of the characters featured in Succubus Heroines Eroge.

Pre-Transformation
She goes to the same high school, Nishizumi, as the main character.

She's also a childhood friend of his, having always lived next door to him.

She has a bright, cheerful personality and she's kind to everyone, but that's not to say she's not without her flaws. She tends to botch things up.

She's been in love with the main character since she was a young girl, but even now she still can't tell him how she feels.

Astaroth
Asuna after having become a succubus.

She was the first victim of a succubus who came from the Demon Realm. Her love for the main character hasn't changed, and she's still overwhelmingly bright and cheerful.

For a succubus, she is obedient and easy to manipulate. She is extremely dedicated to pleasing the main character, and to that end, she'll do whatever it takes. In order to make him a harem, she's going around and sleeping with other girls close to the main character, turning them into succubi.

When she interacts with the main character, she becomes a pure masochist, and she's happy no matter what is done to her as long as he's the one doing it...