[@Zarkun][@Caits][@Lugubrious][@Joshua Tamashii][@soren]
Alright, I guess I'll throw this out to the others as well. Ariel just gained access to magic that likens her to a newborn spirit. As such she could be summoned and contracted (so long as she's in spirit form). Not going to define how to summon her as I want to see what you guys come up with. But everyone should notice the unusual appearance of a new spirit in the world. Since she's a blank slate in the way of spirits I might have her change slightly based on who summons her. Not sure. Take it or leave it, only one can get a contract.

Looks like Gideon, Gabriel, Michael, and Amelia could potentially summon Spirit Ariel. Correct me if I'm wrong.