Ravencrown answered Ace's question with a hint of intricacy, "It was in the legacy we acquired. The owner of the legacy left a message for those who might stumble upon it if they're not the Heaven's Stealer.
"In the message, the owner expressed that the 'Owl' is the hallmark of Heaven's Stealer, and it'll only appear in the place of theft, and on victims of Heaven's Stealer. Furthermore, there was even an image of the 'Owl' etched in the second-level entrance, which almost matched yours.
Lastly, the owner also specifically requested to be informed about this legacy to Heaven's Stealer if the inheritor found any trace of it or simply kept passing the legacy among our descendants until Heaven's Stealer emerged.
"That's why we also designed our hallmark, the 'White Raven', like the Owl we saw in the legacy grounds. We've been hoping to draw Heaven's Stealer's attention, but thousands of years passed, and there's no clue.
