Origin:
Big Bird was a bird who, along with Punishing Bird and Judgement Bird, protected the Black Forest from hostile monsters. Big Bird wandered the forest warning people about a "monster". Judgement Bird gave Big Bird its eyes so it could see farther to seek trespassers and could protect the forest more effectively. One day, someone questioned 'What if the monster came at night?', and Big Bird, worried, made a wick with all of its feathers, stripping itself to its skin in order to create an everlasting lantern to see through the night. Big Bird then wandered the forest and thought of a solution to the monster problem; it believed that killing humans and other creatures would "save" them from dying to the monster. At the end, when the forest was about to enter into total disorder, Big Bird, Punishing Bird, and Judgement Bird decided to merge their forms to protect the forest more effectively. This created a new bird, but instead of protecting the forest, the bird destroyed it. It is unknown when the birds decided to separate themselves.
When Lobotomy went to the forest to verify the tale, they couldn't find any "monsters" or creatures; the only thing left was Big Bird.
Big Bird's habit of killing people in order to prevent them from being killed more brutally carries over into X's Facility, where it will try to kill researchers in an attempt to provide salvation from the usually gruesome deaths caused by other breached Abnormalities.
Story:
"A large, many-eyed bird that patrols the dark forest with an everlasting lamp. Unlike regular birds, it lacks wings and has long arms instead with which it can pick things up."
"...(Omitted) would stare intently at anyone it found, young or old, and bite their head off. There is a tale of a beast that lies in the deepest, darkest part of the forest who dazzles creatures away never to be seen again. To protect all creatures from the beast, the big bird burned all of its feathers to make a wick, and then made a lamp that would burn forever. With this eternally lit lamp, the big bird wandered the forest, warning the creatures to not stray too deep into the trees. Thanks to the large bird, fewer creatures fell victim to the beast in the forest. However, it was still concerned for the creatures still being killed by the beast. An idea struck the big bird’s mind: “If I kill the creatures first, then no one would be killed by the beast!”
I ran out of space