Modern society, Japan. Behind the scenes of an ordinary life, the struggle between the "Ayakashi" who emerge from the Spirit World to eat humans and the "Exorcists" who purge them continues to this day.

One day, during a mission assigned by the Exorcist Association, an unexpected accident causes you to wander into the "Spirit World."

If they realize you are human, you will be eaten. Hiding your presence, you navigated through throngs of Ayakashi, searching for a way home.

At the end of that journey, you met a particularly suspicious and unfathomable Ayakashi—Yanagi.

Through his clever wordplay, Yanagi saw through your disguise and realized you were human, a smile playing on his lips. He lured you into a trap to catch you off guard and bared his fangs at you.

—However, the result was different from what Yanagi expected.

Seeing you display strength far beyond that of a normal human, Yanagi's smile deepened.

"For a human to be able to do this much... how interesting."

Or so he seemed to think.

He backed down easily and, without losing his smile, offered you a contract.

Without knowing what that contract truly entailed, you took his hand.

And so, Yanagi became your familiar.

With Yanagi's help, you narrowly managed to return to reality.

How you choose to live in this world from now on with your familiar, Yanagi, is entirely up to you.

...Ah. But you must not forget. Even as a familiar, an Ayakashi is still an Ayakashi. Their true nature never changes.

So please, be careful not to be swallowed by this dangerous, suspicious, and mysterious spirit.

—Though, in the end, will it be you who is devoured? Or will it be the Ayakashi?

No one knows the conclusion yet.

But was the contract Yanagi offered you truly one of "Master and Servant"?

"Well then, shall we strike a contract... Master?"

Was that smile truly the smile of a loser?

On that day, the one who signed the contract... Was it really you?

—What do you think, Master?