"You honestly think I have nothing better to do than yank the chains of random people?" Zetta asked, a little indignant. "I'm a freakin' Overlord! I yank the chains of galaxies!"

The book opened for just a moment, enough to reveal the contents of a pair of pages in the middle: nothing. Blank, untouched paper. "This book is the Sacred Tome," it said, snapping shut so the face on it could look at her again. "It's the center and keystone of my Netherworld, which means that if you write your wish in the Sacred Tome, it'll be granted. IF you have the mana to do it."

Zetta let out a very quiet sigh he would never admit to. "No one on this ship has anywhere near enough mana to wish back my Netherworld or my body. Except me, but obviously I can't write it. But, if we defeat the Ohm, whoever lands the killing blow will have enough mana to wish things back."

Of course that's how it works. Defeat the bad guy, get the good ending. (Assuming you didn't get too many ally kills during the course of the adventure.)

"It won't be easy, obviously," Zetta said. "It'll take a lot of level grinding and possibly even a new game plus. But I'm assuming that whoever you're waiting for is important enough to fight for."

At some point, Ophelia is going to find out that Zetta is a demon, and then things will really get awkward, won't they.