Atsuhiro Sako, alias Mr. Compress, hails from a lineage of thieves as the great-great-grandson of the Peerless Thief, Oji Harima. This heritage fuels his criminal life and ideological crusade against a corrupt hero society, motivating his membership in the League of Villains to redistribute wealth and challenge systemic injustices. Tall and slender with pale skin, curly brown hair, and distinctive semicircular brown eyes, he consistently wears a black balaclava beneath various white masks featuring geometric designs. His typical attire includes a dark orange shirt, green-striped bolo tie, black waistcoat and trousers, knee-high white boots, red gloves, and a brown top hat adorned with a red ribbon and feather. After losing his left arm to Overhaul, he uses a Giran-provided prosthetic. His personality marries theatrical showmanship with calculated cunning. A former stage magician and escape artist, he frequently monologues, employs dramatic gestures, and revels in misdirection, though this flair occasionally undermines him, as when prolonged taunting allowed adversaries to corner him during the Forest Training Camp. Despite claiming an aversion to attachment, he demonstrates fierce loyalty to the League, leaping to avenge Magne’s death despite personal risk. He mentors younger members like Himiko Toga and acts as a voice of reason, though he exhibits occasional rudeness and impatience with impulsive allies. His dialogue often critiques societal conformity, emphasizing individual choice. His Quirk, "Compress," allows him to shrink objects or living beings within a spherical radius around his hand into marble-sized spheres, negating their Quirks and reducing their weight for transport. Activation requires direct touch; decompression occurs via finger snaps, enabling selective or mass reversion. Tactically, he uses this for stealth captures, environmental manipulation like launching vehicles with decompressed boulders, and precision maiming—exemplified by tearing off Overhaul’s arm. The Quirk relies on his arms for activation; losing his left arm restricted him to his right arm only. He compensates with decoy marbles, evasion tactics, and enhanced agility, dodging attacks like Shoto Todoroki’s ice. His Quirk also facilitates infiltration or escape by compressing himself or tunneling through solid materials. Key conflicts showcase his resourcefulness and loyalty. At the Forest Training Camp, he captured Katsuki Bakugo and Fumikage Tokoyami using misdirection before U.A. students intercepted him. During the Shie Hassaikai Arc, Overhaul destroyed his left arm after Magne’s death; he later exacted revenge by compressing Overhaul’s arm during a prison transport ambush. He killed Pro Hero Snatch by compressing him amid Dabi’s flames and aided the League’s merger with the Meta Liberation Army, becoming a Paranormal Liberation Front lieutenant. His pivotal moment came during the Paranormal Liberation War’s climax: evading Best Jeanist’s bindings, he compressed part of his lower back, permanently maiming himself. He freed Tomura Shigaraki, Spinner, and Skeptic from restraints, sacrificing more of his body before defeat. Here, he revealed his Harima lineage and performed his "final act," compressing allies into marbles for safekeeping to ensure their escape despite his capture. Following the Final War, authorities arrested him alongside Spinner as one of the League’s two surviving members. His legacy endures through his commitment to his ancestor’s ideals and his role in pivotal villain operations.