"I-I can't afford to die," muttered Toya, a descendant of the Amagi family who ran a Youkai extermination shop. For him, exterminating youkai is a job and a means of revenge.

Amagi Shinichirou was killed by a Youkai ten years ago. In order to avenge the man who was his own father, Touya goes out to exterminate Youkai with the demon "Kikou" today as well, but he is unable to catch his enemy's tail.

However, one day, a youkai called "Seku" appeared in front of him. Seku, who had the
appearance of a human boy, spoke to Toya with a meaningful smile., "... 10 years ago."

[Translated from official website]