Animal X

27 year-old Ayukawa Yuuji is a mild-mannered biology researcher with a fiancée. After agreeing to being a test subject for a new drug, a young man breaks into his room and declares, "You're going to have my kid!"

Yuuji suddenly finds himself the sole target of a lost race that turns into dinosaurs, an extremely scary woman with a Goddess-Complex, the yakuza, a mad scientist and one 17 year-old boy who really, really, really wants to sleep with him.

Series:

1. Aragami no Ichizoku (4 volumes)
2. Daichi no Okite (2 volumes)
3. Genshi Sairai (10 volumes)