A Background Disciple Witnesses His Master Falling in Love with Himself, Start to Finish

[The blurb may change before the story begins, so feel free to remove it from your collection.] For the sake of his grand ambitions, the Demon Realm's master opens a secret identity in the righteous path. While suffering from amnesia, he falls in love with his secret identity among the righteous, but can only stab himself, torment himself, and even has to figure out how to kill himself. And so, Lin Zhou, an ordinary disciple who transmigrated into a book, finds a new source of amusement in his dull, interminable life. Theme: Saving people means saving their hearts