He was the egg of the Black Goat. Sarutahiko Aikawa hates his mother, but when those killing impulses start appearing, things start slipping, and something he never wanted starts happening. Disclaimer: The Black Goat's Egg does not belong to me, it belongs to Ishida Sui and Tokyo Ghoul.
The "Black Goat" is a serial killer that kills without motive, brutally, but precisly. When her son finds out about it, he's disgusted and runs away from home. Later on, he finds out that he's the same as his mother; that he has murderous drives. Again, he's disgusted by it and tries to repress it... My vision of Sen...