As a young child, Takashi Natsume believed his ability to see youkai to be nothing but a curse. Now a high school student, Natsume has managed to heal from his old wounds and form unbreakable bonds with humans and youkai alike. Natsume's newfound friendships—including the one with his spirit bodyguard Madara, nicknamed "Nyanko-sensei"—are often interlaced with his duty to return the names of the spirits written inside the Book of Friends, his late grandmother Reiko's keepsake. While more remarkable youkai reach out to him, Natsume discovers that he still has much to learn about the world that surrounds him.

By the mid-21st century, Tokyo's criminal underworld is ruled by Demon Lords—crime bosses who have undergone ether enhancement surgery, granting them terrifying superpowers. The only ones who can take them down are Heroes, bounty hunters who boost their own ether powers using the drug E3 (E-Three). With legalized killing as part of the job, being a Hero is less about justice and more about survival. Yashiro, known as the Reaper, is one such Hero—an independent enforcer who works alone. That is, until Jougamine, a high school girl and self-proclaimed "apprentice," forces her way into his life. Reluctantly taking her under his wing, Yashiro soon finds himself caught in a whirlwind of deadly conflicts.

On an unknown continent, there is a city called Satellite City No. 9. In this city, a screw straightening worker named Rui Li at the screw factory gradually realizes the unreality of the city in her monotonous daily work. With the help of a mysterious character named "Anull", Rui Li gains the superpower of "transformation" and becomes the thief "Sirius", secretly taking action to escape from here. When the truth of the world finally unfolds before her eyes, Rui Li discovers that her real battle has just begun.

Second season of