The main protagonist of the series. He is experiencing a form of "Escapism", or something similar, where he wishes he could go to a foreign place, far away. Similarily, his two best friends, Chouta Segawa and Karube Daikichi, also long for this far away place.

One day, when they are out, they catch a glimpse of fireworks, almost blinding them. After this explosion, they get suddenly thrust into a seemingly different world. Although the city looks almost the same, it appears deserted and in ruins. After stumbling across a woman, they accidentally enter a "game venue". Without much information as to what is happening, they start playing the game after the rules are stated, not knowing the deadliness of these so-called "games".

Arisu didn't go through a very happy childhood. His mother died at some point, leaving him and his little brother to his father. From a young age, these two siblings were always compared to each other. While Arisu was the average "delinquent" and unsuccessful son of the family, his brother excelled at everything he tried. This created some kind of distance between them, causing the father to grow fonder of the younger sibling, while calling the other a failure.

It is later revealed that other people have also entered this deserted place. These summoned people are called "players". Their only chances of survival are to enter these game venues that appear all over the city.

These games come in 4 genres (Spades, Diamonds, Hearts and Clubs), with a difficulty ranging from 2 to 10. Spades focus on the physical aspects of the game, Diamonds focus on situations where you need intelligence to win, Hearts focus on the psychological parts of the game, and finally, Clubs focus on the balance of the required skills, and the cooperativeness of players.

Whenever a person wins a game, their allowance of days in the Borderlands extends, depending on the difficulty of the game. If a players doesn't participate in any games and their remaining days are spent, they are killed by a laser beam.