Breaking Every Bad Ending

After transmigrating into the world of a game, Ain discovers that he has brought along his fully maxed-out New Game+ account. The account is his. The skills are all unlocked. His build is fully optimized. There's just one problem... Why is his mana bar completely empty? "You expect someone with no mana to fight the first act's final boss?" "Wait... the second act's boss is the heroine's closest friend?" "What do you mean every single ending in this game is a bad ending?" "Is the game broken, or am I?" The saintess is nailed to a cross in the name of redemption. The witch is sacrificed to an Outer God. The academy's dean gives their life to save their students. Faced with one tragic CG after another, Ain makes up his mind: "If it's not an ending I like, I'm going to rewrite every last one of them!" ... "Hold on... nobody told me casting spells uses my mana!"