Rumi Usagiyama/Relationships

Endeavor
There has hardly been any interaction between these two heroes, yet Endeavor feels he owes Rumi. After he and Hawks ended up wounded and tired after their fight against Hood, the villain Dabi appears ready to attack them taking advantage of their weakness. Fortunately, Rumi leaps in before he could attack and stops Dabi in his tracks, who is forced to flee from her.

A month later, during the Jaku Hospital Raid, Rumi was grievously wounded from her solo fight against four High-End Nomu. Endeavor took it upon himself to help her and cauterize her wounds. Endeavor reminded her of a debt he owes her after Kyushu, so she can't die on him. Mirko kindly replied he doesn't owe her nothing. Endeavor also took care of Rumi by bringing her to safety after Tomura destroys the hospital with his decay.

O'Clock
While still a hero in training, Rumi met the hero, O'Clock, after she broke into the Underground Masquerade, challenging everyone to fight her, causing quite a stir. When All For One used his Quirk to steal the powers of those attending the event, O'Clock prevented Rumi from being one of his victims. Recognizing her talent as a fighter, O'Clock requested her assistance in order to flee from there.

Rumi assisted O'Clock at all times during the escape and even saved him when he was about to be defeated by the Hooded Man. Still, O'Clock's concern for Rumi's well-being made her feel upset, demanding to be taken seriously. Following the crisis, before separating and taking different directions, O'Clock thanked her for all her help, assuring Rumi that she would be compensated for helping a Pro Hero, but Rumi declined the offer, saying that she will ranking it on her own without the helps of others.

Katsuki Bakugo
Although they never met directly until the Final War, she and Katsuki have similar personalities that often clash, due to them both being headstrong and impulsive. She ignores Katsuki when he becomes upset at her for not using his full hero name, which Mirko just shrugs off. This leads to petty arguments between them. Nonetheless, they were willing to put their argument and petty differences aside to defeat Tomura Shigaraki. When Tomura killed Katsuki by punching his chest that bursts his heart, Mirko become infuriated and goes all out against him, despite losing her right forearm. Even now, she still has some regrets for being responsible in Katsuki's death, stating that if she was just a little faster and killed Tomura back during the Paranormal Liberation War, none of this would happen.

The Rapper
The same day that he met O'Clock, Rumi also met Kendo Rappa, who was an underground wrestler under the name, the Rapper, who was participating in the Underground Masquerade at the time, and who was also helping O'Clock escape. Initially, their first meeting didn't start off on the right foot, partly because Kendo considered women incapable of get his manly philosophy, and partly because soon after they met, they started to have an argument about whether "Kick Power" or "Punch Power" is most important in a fighter.

Despite this, both did not hesitate to collaborate together in order to escape the Underground Masquerade, protecting each other, so they began to respect each other fighting skills. When the crisis is solved, before leaving to continue her career as a hero, Rumi asked Kendo what he planned to do, to which he replied that he would continue to be an underground fighter. Knowing that that implies that it made him a villain and that she would be a hero, maybe someday they would have to face each other, so she promises him that she’ll be sure to save her less deadly kicks for guys like him.