Seras

One of the first semi-successful human/demon hybrids, she's still very early in the physical changing process. She always had a fascination with angels and demons, and, after borrowing a demon summoning book, she found herself in a very sticky situation......

After falling head over heels for a summoned demon, she willingly let the demon subject her to the long, painful process of being slowly shifted into  full blooded demon..... 

She's constantly in pain, the demon blood coursing through her veins causing sharp jolts of pain constantly, but she tries not to show it.