Unemployed and residing with his mother, Ryouta Sakamoto excels as Japan's top Btooom! player, an online game. His mundane routine shatters when he awakens on a remote island, marked by a mysterious green crystal on his hand and no recollection of the past. Shockingly, the game he mastered is now a grim reality, where survival hinges on killing fellow participants to claim their crystals. Reluctant at first, Ryouta embraces violence as a means to escape when faced with ruthless rivals. Alongside Himiko, another Btooom! enthusiast, they navigate treacherous alliances and deadly challenges, inching closer to unraveling the enigma behind this lethal game.