Celestia

Celestia is the daughter of Merlin who resides in the Forbidden Library. She takes the form of an owl that you can interact with if you encounter her.

Upon interacting with her, you have the option of petting her or breaking her shield. If you pet her, she will drop ingredients/item. If you break her shield, you are given the option to kill her or not. If you choose not to kill her, she will drop ingredients. If you choose to kill her, you will be given Owl Remains as a crafting item. This can then be crafted into a very strong equip item: Murderer's Ring, which gives +10 Mixed damage, +10 Mixed defense, and a periodic laser effect.

Note: Killing Celestia is NON-REVERSIBLE, short of resetting your entire save data.