Secre Swallowtail (Nero)

The little bird that has followed Asta since the dungeon is in fact Secre, the first Wizard King's sealing mage, alive for five hundred years.

Accused of forbidden magic for saving Lumiere, Secre turned herself into an anti-bird and waited half a millennium. Her Sealing Magic can stop, reopen and rearrange any spell — she is the one who frees the elves' souls from the Magic Knights' bodies and breaks Zagred's manipulation.