In Xialai, Kivotos, a teacher suddenly appeared. Some say he's a perverted adult who uses his position to give orders to students to satisfy his own selfish desires. Others say he possesses great power and will use it to eliminate anyone who might stand in his way. Others say he's a master strategist who can easily outmaneuver his enemies. But... Hayase Yuuka says he always secretly uses money to buy all kinds of childish toys. Namishio Noah says he often works late into the night to complete his work. Sorasaki Hina says... , he will definitely show up when the students need him the most. Hoshino Takanashi said that even though he sees through the hearts of students, he never discriminates against them. Alice said that he is the mascot with a charm value of 99. Mika Seizono said that he is the prince in her mind. As for him… "He existed before, but he is gone now." Lin En pushed his glasses and answered Yuuka who was standing in front of him seriously, "Teacher Lin En, what is this?" When Lin En saw the "Little Liu Bei" in the hands of Kurosaki Koyuki, which he took out from his drawer, he knew that he was finished.

Yuuji Sakai, the usually vacant and somewhat weak protagonist, lives an ordinary life until the sudden appearance of a monster disrupts his ordinary life. Under the setting sun, Yuuji is suddenly attacked by an alien monster that transforms human "existence" into spiritual fire and then devours it.

At this time, a girl who called herself "Flame-haired and Burning-eyed Slayer" appeared and rescued Yuuji from the monster's mouth. Yuuji Sakai named her Shana based on the name of her large sword.

She told Yuji that his life was about to end - it turned out that outside this world, there was another world called the "Red World". In order to realize their ambitions, the people there took away the world's original power, the "power of existence", from humans one after another, and Yuji was one of the victims.

After the Crimson Apostle took away the "Power of Existence",...