With an impossible grin and the cheerful voice of a children's television host a creature made Yui an offer she never thought she'd hear: any wish she wants, granted.

There's only one catch.

Every wish comes true literally. And all it asks in return is one small favor, plus her help whenever it's needed.

Yui asks for one more night with her sister.

She gets every night instead.

The creature calls itself a helper. It promises there's nothing to fear.

Maybe Yui should be more careful. Maybe she should ask questions.

But when something offers you the one thing you've wanted most, how much does caution really matter?

And what, exactly, does a creature like that consider a small favor?