The Serpenters, twin brothers Ena and Dio, serve as antagonists within the anti-Quirk terrorist organization Humarise, led by Flect Turn. Despite possessing Quirks themselves, they joined Humarise because they believed Flect Turn would spare them from the organization's planned genocide of Quirk users, allowing them to survive in the rebuilt world. This choice prioritized self-preservation over ideological alignment. Physically identical, both twins have average builds, fair skin, indigo bowl-cut hairstyles, yellow reptilian eyes framed by dark purple markings, and large fangs. They wear simple red and white tunics and gray boots resembling snake skin. When enhanced by Trigger, their features become more viciously snake-like: facial markings darken, hair spikes, mouths stretch to their ears, and teeth sharpen. Their personalities mirror each other, marked by extreme devotion to Flect Turn and erratic, excitable behavior. They display eagerness for combat, deriving manic pleasure from fighting and attempting to kill opponents, often laughing uncontrollably during battles. Their loyalty to Humarise's cause coexists with their Quirk usage, justified by their conviction of being "chosen" survivors. Flect Turn deployed the Serpenters alongside Leviathan to intercept protagonists Izuku Midoriya, Shoto Todoroki, and Katsuki Bakugo during their assault on Humarise's headquarters. Katsuki Bakugo engaged the twins. When Bakugo questioned their allegiance to an anti-Quirk group, they asserted their privileged status as survivors chosen by Flect Turn. Their coordinated fighting style and Quirk proficiency allowed them to inflict significant injuries on Bakugo through swift strikes and grapples. After Bakugo collapsed a column onto them, they injected Trigger to break free, gaining enhanced physical capabilities. Trigger amplified their Quirk, enabling them to generate up to seven extendable blade appendages simultaneously—four from their upper backs and one from their mouths—increasing offensive pressure. Bakugo ultimately defeated them by slamming them into a cavern wall and unleashing his "Howitzer Impact" Ultimate Move, burying them under incapacitating rubble. Following Humarise's defeat, they were apprehended. Their shared Quirk, "Sword Kill," transforms their arms into extendable, whip-like bellow swords used for offense and aerial grappling. Trigger augmentation temporarily boosts their speed, strength, and agility while expanding their Quirk's capacity to generate blades beyond their arms.