[Soji]

Reaper@

Spoiler for spoiler:

If is who I think....then that one was a fake. Kamito it's the only true male spirit contractor .(and probally the reaincarnation of the 6 spirit king like the demon king was).This one that you say was a experiment and can use the spirit only once from what i recall.
Also Est have a curse so it's good that she is in this weaken state for now. Otherwise she would kill kamito like her old master.And that's was one of the reason why she don't want to come back to kamito in vol 6.