In a world threatened by alien forces, Bastioners, skilled fighters wielding the enigmatic power of Aegis, defend their realm. Aegis bestows immense strength but can only be wielded on others, prompting fighters like Yorino Aratsugu and Yoko Kaminoi to team up. Once Yoko's protector, Yorino now finds herself trailing behind in all but combat prowess. As they advance as Bastioners, Yorino grapples with feelings of rivalry towards Yoko, her closest companion, and navigates the intricate emotions blossoming within their friendship.