In 3813, people would always disappear at midnight and either return safely or never return, but those who came back were mentally disturbed.
Until Su Xi also disappeared at midnight, she returned safely without any fear. She was unwilling to tell anyone what happened when she disappeared.
She also made many "good friends" in the secret room, but it seemed that "she was the only one" who survived every time, but a few of them also survived.
The people who disappeared are all related in reality, but they may have forgotten it.
And the people who survive to the end are the "winners".
Intention: Wisdom is the weapon that can survive to the end