The problem is that nobody knows if the book's power is enough to save two people, and neither is willing to share with the other
Not very interesting, you say?
And if they are ghost sweepers, professional exorcists exterminating evil spirits and demons?
Huh, not inventive enough?
Then what if the man is a total pervert, beyond hope of any salvation, and the woman is a total hottie?
And there are more babes to come!
What? Sounds like a standard harem manga?
Ok, then let's suppose that the woman is as avaricious as the man is perverse
And she knows how to use her charms to force the man into suicide missions for a starvation wage.
Still missing something?
Then how about a dark, hidden scheme that has been running for ages, which of course can't ignore the woman, who is one of the most powerfull ghost sweepers alive?