Murakami Yasuharu is a subject of bullying.

Getting ignored, being treated harshly, for so long, he had endured, but they gradually escalated. However, there is no one around him to rely on, and eventually, his spirit is cornered, and exhausted. In the midst of his despair, looking for an easy way to end his life, he comes across a website about demon summoning. As he reads through the article, "If you want to kill yourself, then take revenge," and with that sentence, he decides to give it a try. Although he is skeptical, he gathers the materials needed for the summoning, at the cost of his own soul, he tries to summon the demon.

However, a mysterious monster appears. Panicked, Yasuharu runs out of his house, and gets into an accident, before losing his life instead of his soul, the creature that he has summoned──the monster merges with him, keeping him alive.

Thus, now merged with the monster and even acquired a special power, Yasuharu begins to take revenge on the person who bullies him.