Atsuhiro Sako, alias Mr. Compress, is a 32-year-old male affiliated first with the League of Villains and later the Paranormal Liberation Front. He is the great-great-grandson of Oji Harima, the historical "Peerless Thief" who targeted corrupt heroes during the Hero System's early establishment. This lineage fuels his commitment to exposing societal injustices perpetrated by hero institutions, driving his criminal path. Before villainy, he worked as a professional entertainer, integrating his stage magic and escapology expertise into his criminal activities. Physically, he stands tall and slender with pale skin, semicircular hazel eyes, a pointed nose, and curly brown hair. His signature attire features a black balaclava beneath a white geometric mask, a dark orange shirt, green-striped bolo tie with an azure brooch, black waistcoat, dress pants, knee-high white boots with black toe caps, red gloves, and a brown top hat sporting a red ribbon and feather. After the Shie Hassaikai conflict, he lost his left arm to Overhaul and uses a robotic prosthetic. During the Paranormal Liberation War, he sustained permanent lower-back injuries while using his Quirk to escape capture. His personality blends theatrical showmanship with strategic cunning. He frequently employs grandiose gestures, monologues, and misdirection during operations, reflecting his entertainer roots. Despite this flamboyance, he serves as the League's primary tactician, known for analytical precision and resourcefulness. He values self-determined ideals over societal imposition, criticizing hero students for accepting externally dictated values. Loyalty manifests in protective actions, like mentoring Himiko Toga and seeking retribution against those harming allies. He holds deep grudges, notably against Overhaul for dismemberment, and exhibits pragmatic ruthlessness in combat. His Quirk, Compress, enables him to shrink objects or living beings within a spherical radius around his hand into marble-sized orbs. Activation requires direct touch; compressed entities suffer no physical damage but lose Quirk access while immobilized. The marbles reduce weight for easy transport and concealment. He selectively decompresses targets via finger snaps, individually or collectively. Tactical applications include: * **Stealth and Capture**: Compressing enemies or himself for covert infiltration or instant incapacitation, used during the kidnappings of Katsuki Bakugo and Fumikage Tokoyami. * **Environmental Manipulation**: Deploying compressed objects as traps, like decompressing boulders beneath vehicles. * **Precision Maiming**: Targeting specific body parts, exemplified by severing Overhaul's arm without causing pain. * **Escape Artistry**: Excavating through terrain or evading restraints via partial self-compression. Limitations include dependence on his arms for activation—reduced to his right arm after amputation—and a range restricted to his physical reach. Overuse risks fatigue, and unsecured marbles remain vulnerable to theft. Additional capabilities encompass enhanced agility for evasion and tree-canopy traversal, plus keen intellect for rapid battlefield assessment and deception, such as creating ice decoys at the Forest Training Camp. Key chronological developments are: * **Forest Training Camp Arc**: He captured Bakugo and Tokoyami using stealth and misdirection. During escape, he concealed the true marbles in his mouth while deploying decoys; Bakugo was later recaptured after interference. * **Hideout Raid Arc**: He explained the League's ideological goals to Bakugo and battled Pro Heroes until Nomu reinforcements arrived, aiding ally retreat via compression. * **Shie Hassaikai Arc**: After Overhaul murdered Magne and destroyed his arm, he later ambushed the yakuza leader during police transport. Collaborating with Tomura Shigaraki, he compressed Overhaul's arm as retaliation. * **Meta Liberation Army Arc**: He expressed dissatisfaction with the League's petty crimes post-Shie Hassaikai and fought in the six-week conflict against Gigantomachia. He identified Giran's abduction via news verification. * **Paranormal Liberation War**: As a lieutenant, he crippled himself escaping Best Jeanist's restraints, freed Shigaraki and allies, and was ultimately apprehended by Mirio Togata. Post-arrest, he was imprisoned alongside Geten, becoming one of the League's two surviving members after the Final War. Interpersonal dynamics highlight loyalty to Tomura Shigaraki as a leader worthy of continuing Harima's legacy. He acted as a father figure to Himiko Toga, advising caution. He shared sarcastic camaraderie with Dabi, collaborating to defeat Pro Hero Snatch by compressing him into blue flames. His relationship with Twice involved mutual respect despite criticizing Twice's emotional attachments. He held deep animosity toward Overhaul, culminating in vengeful mutilation.