Atsuhiro Sako/Relationships

Oji Harima
Although not that much is known about his relationship with Oji, Atsuhiro appears to hold great respect towards his great-great-grandfather. He also holds great pride in being related to Oji. For that reason, Atsuhiro is dedicated to carrying on Oji's legacy by joining the League to fight against such a corrupted hero society and wealthy heroes, exposing the injustices of hero society.

Tomura Shigaraki
Mr. Compress appears to have a sense of loyalty to Tomura Shigaraki and the rest of the League. He is dutiful in carrying out objectives. During the forest training camp, Mr. Compress captures not only Katsuki Bakugo but also Fumikage Tokoyami believing him to be beneficial to the group after seeing Dark Shadow's rampage take out Moonfish. When Katsuki is rescued during the All Might and All For One battle he is first to respond that they can't let him escape and asks who has a long-range attack, knowing how much Tomura wants to keep Bakugo.

Atsuhiro follows Tomura's commands and doesn't hesitate to aid him in battle, as seen when the League was battling Gigantomachia for over a month.

Vanguard Action Squad
He acts as overseer for the other members. He regularly contacts them after All Might defeats All For One in the Kamino Incident causing the League to disperse to avoid capture. Mr. is usually the voice of reason in the League, just like the time he advised against engaging the Meta Liberation Army, considering their number advantage.

Himiko Toga
Atsuhiro acts like a father-figure or overseer towards Toga. He often takes time to explain things to Himiko Toga such as when she asked about what Yakuza was and the difference between them and the League. He tends to call himself "Old man" when talking to Toga and doesn't hesitate to pay her compliments. When Mr. addresses Toga, he usually calls her "Dear".

The moment the Paranormal Liberation War begun, Toga and Mr. were walking around in a corridor in the villa and were both caught off-guard by a hero, who apprehended them. However, Twice appeared and saved them, but melted away, prompting toga to go on a suicidal killing spree, while Compress tried to stop her from doing such a dangerous act.

When the Paranormal Liberation Front's lieutenants were riding on Gigantomachia's back and Toga was pesnive, while standing on the egde, Compress told her to be careful and guessed correctly that she was thinking about the U.A. Students she loves. When Toga was about to jump off Gigantomachia, Mr. told her to stop because it's dangerous, showing that he genuinely cares for her life.

Twice
Mr. Compress had a sense of good camaraderie with Twice, as shown when he was saved by him during the Paranormal Liberation War, he was joyed to see him and truly believed that he would turn the tide of battle. When the clone started disappearing, he realized that Twice was killed, and showed signs of grief and shock seeing his teammate die.

However, it is to be noted that Mr. Compress criticized Twice for being too attached and "buddy buddy" to people when Twice insisted that the League go and save Giran despite the danger. He also noted how Twice would fighting for his friends, since that's what Heroes usually do, and he was still a villain.

Like the whole League, Twice though of Mr. Compress as a true friend.

Dabi
Dabi and Compress seem to have good camaraderie as they've teamed up on a few occasions. One of the notable team-ups involved them both using their Quirks to take down Snatch when confronting Overhaul. They have some kind of sarcastic relationship, as seen during the Revival Celebration, where Compress asked Dabi for his aid, but he declined request, prompting Compress to ask why is he so unfeeling, while in reality Dabi noticed Twice's clones coming to a rescue. Dabi also enjoys mocking Compress when the opportunity comes by, notably when he calls the latter out for doing nothing during the clash against the Meta Liberation Army, to which Atsuhiro replies acknowledging the fact and sarcastically brushing it off.

Mr. Compress also seems to like returning the mocking right back at Dabi, when the latter carelessly burned Kamui Woods and Midnight, ignoring the fact that Midnight was still going to put gigantomachia to sleep, to which Mr. quickly reacts. Mr. scolds Dabi for underestimating the Heroes, leaving him with an unamused expression on his face.

Magne
While Mr. Compress didn't show any trace of a close relationship with Magne, he was the first to react when Overhaul killed her which cost him an arm.

Overhaul
Mr. Compress hates Overhaul after he destroyed his left arm while trying to stop him. After the fall of the Shie Hassaikai and the capture of Overhaul, the League assaults the police van transporting Overhaul to a hospital. Tomura tells Overhaul he hates his 'high and mighty' attitude. Mr. Compress agrees with the statement and compresses part of Overhaul's left arm, severing it at the wrist as an act of retribution.