My own #Alice theory. This kid is Yoon Taeyi. When she traveled back to 1992 she probably forgot the memories she had as a kid due to trauma. She is on her 30s and became a professor in 2020. She's the one who has the last page of the book of prophecy.

So after her father got killed in 1992. She got adopted by the Yoon Family.

She then worked in Alice which exists in 2050 she will be 60s by that year but looking how young she is ,she probably time travelled to the future. Maybe in 2025 something.

So when her son met her in 2020. She doesnt know him yet. Cause she wasnt with Alice still in this time.

When she got killed in 1992, she knew her present self is out there.She knew her son will meet her present self sometime in the future (maybe becoz it happened to her already since she already spent 2020.) She wants her son to avoid her maybe because of that tragedy (?)

The story of the book of prophecy is about her and Jingyeom. I don't know whats the tragedy but for sure its because they messed up the timeline whicmakes time traveling dangerous. She gave birth to her son in 1992 who is supposed to be born in 2050 and they met again in 2020.

And maybe she stole the book and stayed in 1992. She didnt want Alice to findout about the book of prophecy. She wanted to protect her son.

okay this is my theory for now.