If Rabi has a dark seal, it could very well be 魔. It's the "ma" in both Makai and Enma.
Makai, literally "Evil World", it is a synonym for Hell that emphasizes its nature as a realm of demons. (Rather than Jigoku, which means "prison land" and focuses on it being a place of condemnation for evil doers.) Enma is a name for the Japanese version of the Devil.

