A shy university student in Tokyo, Karen Kohiruimaki stands in stark contrast to her in-game avatar. Towering above all the people around her, Karen's insecurities over her height reach the point where she turns to the virtual world for an escape. Starting game after game in hopes of manifesting as a cute, short character, she finally obtains her ideal self in the world of Gun Gale Online. Overjoyed by her new persona, she pours her time into the game as LLENN, garnering her reputation as the legendary player killer. However, when one of LLENN's targets gets the best of her, she ends up meeting Pitohui, a skilled yet eccentric woman. Quickly becoming friends with Karen, Pitohui insists that LLENN participates in Squad Jam, a battle royale that pits teams against one another, fighting until only one remains. Thrust into the heated competition, LLENN must fight with all her wit and will if she hopes to shoot her way to the top.

A new tournament, Squad Jam 3, has been announced in the popular VR game Gun Gale Online. This time, Pitohui, one of the best performers in the previous competition, offers to team up with Karen Kohiruimaki, better known in-game as LLENN, the "Pink Devil." Despite her initial reluctance, Karen agrees to join Pitohui's team, LPFM, since she looks forward to facing SHINC, her rivals from the previous Squad Jam. The newly formed LPFM enrolls in the tournament and is quickly recognized as the favorite to win due to the caliber of its players. As they strive to come out on top and win Squad Jam 3, LLENN, Pitohui, and the other members of LPFM battle against other competitors and tackle unexpected challenges.