My Disciple Is a Monster

The Immortal Lord of Yewu Continent failed to overcome the tribulation. When he opened his eyes, he found that he was actually on the earth... And who is this girl next to me? I don't seem to be favoring any lady, right? Obtaining the memory of this body learns that this girl is his apprentice. After a night of practice, she discovered that she could swallow the night. "How could this happen? This is obviously an ability that only monsters can possess." Even the divine eye cannot see through her identity. What other hidden identity does this disciple have?