During a Tokyo outing with her friend Mana, Riko Morisawa stumbles upon a fateful billboard advertising the famous LBX toys. Despite initial hesitation, Riko acquires LBX kits for her father, leading to a surreal encounter when opening the 'LBX Assassin' package triggers a dimensional shift. Plunged into an alternate Japan's sky, Riko is saved by an LBX exosuit, only to confront menacing metallic beings known as the Mimesis on the ground. Rescued by a group of LBX-wielding girls, Riko joins their ranks in the combat team 'Soukou Musume.' Soukou Musume Senki chronicles their battles, showcasing the bonds forged amidst daunting challenges.