We Promised to Defeat the Demon, but How Can We Use Me as a Power Bank?

Turns out all myths are true! Mythical creatures have existed since ancient times? ! When Chen Yu was most lonely after losing his loved ones, the red-haired woman told him: "As long as the demons in the world are eliminated, the world can be restarted and the dead relatives can be resurrected." Chen Yu didn't find out until the actual battle. Didn't we agree to defeat the demons together? Why are you using me as a magic power bank?