My Instant Death Ability is So Overpowered

Yogiri is a high school student who likes to play games and take naps. During a school trip, Yogiri and his classmates are traveling by bus when they summon to another world by Sage Sion, who suddenly appears. The students recieve the special ability "Gift" by Sion. They challenges to a trial to become "Sages", the higher-ranking beings in this world.

Yogiri and Tomochika try to catch up with their classmates in a certain town. In there, they tricks by a seemingly kind beast folk and attacks by a criminal gang. Yogiri and Tomochika escape their predicament by killing the gang with the "Instant Death Cheat". However, the guards see the whole thing. They somehow manage to lie and are released.

Yogiri and Tomochika visit Hanabusa, a town much like Japan. There, they reunite with a classmate Yuuki Tachibana. Without any greetings, Tachibana proposes to Tomochika to become his lover. Tomochika bewilders and declines the offer. Later, Tomochika seems to have too much free time on her hands at the hotel where she is staying.

Masayuki unleashes zombies on Hanabusa City. He orders by Sage Lain to eliminate Yogiri and Tomochika. In exchange for stopping the zombies, he forces the people to bring Yogiri to him. Under such circumstances, Yogiri appears in front of Masayuki. Meanwhile, Lain is watching from outside the city. She is planning to find out how powerful Yogiri's "instant death ability" is.

Yogiri and Tomochika depart for the capital. Early in their departure, Yogiri falls asleep in the car. During his sleep, he dreams of the events of his childhood when he names AΩ (Alpha Omega) and quarantines in the "Independent Higher-Order Lifeform Research Institute". Later, the car in which they are all riding plunges into a dragon territory.

Yogiri and Tomochika are involving in a trial to decide the Knight of the Divine King, who fights against the Dark God. Wanting to get to the Capital as soon as possible, they go down to the lowest floor of the 100-floor tower. On the way, Teresa, a former knight who enjoys hunting participants, stands in front of them. Afterwards, Yogiri and the others reach a safe zone and rest for a while.

Theodisia is a girl who participates in the trial of the tower in search of her missing sister. She asks for help from Yogiri and Tomochika, and they agree. They head for the basement where Theodisia's comrades are said to be held captive. Meanwhile, on the top floor, the Dark God's spawns attack the tower.

Yogiri's childhood... Asaka Takatou has been employed by the Independent Higher-Order Organism Research Institute and entrusts to take care of Yogiri. One day, Asaka takes a break and goes out for the first time in a long time. However, she kidnaps by a certain institute that is after Yogiri. Yogiri waits alone for Asaka's return, but showing no signs of coming back.

Yogiri and Tomochika arrives in the Kingdom of Manii Royal Capital and meet up with their classmates. They orders by the King to defeat the Dark God which has sealed away in the Underworld. In the meantime, several classmates who knows Yogiri's identity approach him.

Ayaka Shinozaki is taking revenge against her classmates who abandons her. As an artificial human, she takes on the power of a dragon. Gaining overwhelming strength and kills her classmates one by one. She even kills the King of Manii, who is an obstacle to her goal.

Sion appears once again in front of the Sage Candidates. She believes that if this continues, no new Sages will be born. And then, she orders the candidates to kill each other until there is only one remaining. Some candidates try to resist the unreasonable order, but...

Shinozaki wins a fierce battle against her classmates, but then, 60% of her body destroys. With her last ounce of strength, she transforms her body into a dragon and begins attacking her classmates again. Meanwhile, Yogiri and the others intend to leave the Selection area and lure Sion out.