“I’ll become your ideal girlfriend. So please, just give me one more chance.”

The one who appeared before Hiroto Takenouchi saying that was Chise Koumoto, his clingy ex-girlfriend whom he should have broken up with yesterday… or rather, something else wearing her form.

Calling herself Eiko, her true nature is that of a shapeshifter: a shadowy aberration that devours other beings and blends into human society by mimicking them.

Though she has taken Chise into herself, Eiko claims she hasn’t absorbed her completely, instead keeping her inside. She makes a demand:

“I don’t care if it’s only for a limited time. I want to live as your girlfriend. If you do that, I’ll safely release Chise.”

And so begins a temporary, make-believe romantic relationship born from that promise. Yet once they actually start dating, Eiko turns out to be even more in sync with him than Chise ever was.

Through his interactions with Eiko, Hiroto’s exhausted heart is soothed, and he begins to remember what it feels like to like someone, to feel fulfilled by it.

But precisely because of that, there will come a day when he must face it.

The truth that the girl before him is an inhuman being, living by principles different from those of humans.

And the fresh yet bitter memories that have shaped Hiroto into who he is…