Mirai Sasaki/Relationships

All Might
Nighteye was a huge fan of All Might prior to their partnership. He wanted to be of use to his hero and approached All Might to be his sidekick. Initially, the hero refused because of his rule to not take on sidekicks. However, Nighteye was incredibly persistent and All Might finally accepted him to be his sidekick. From then, they worked together as a team for five years with Nighteye supporting All Might with his intellect. Six years before the events of the story, they had a falling out when their values conflicted in regards to All Might's injuries.

It was around the time after All Might had gotten his wounds from All For One, and Nighteye pleaded with All Might for him to retire and find a successor with similar traits to him. Nighteye believed that by retiring, All Might's legend would live on, and that he would only damage the citizens and other heroes who look up to him if he pushed himself. All Might refused his partner's advice for fear of another villain as powerful as All For One rising to power in his absence.

During their conflict, Nighteye brought up a future he saw of All Might via his Quirk, Foresight. According to All Might, Nighteye saw a future where All Might would clash with a villain and meet a gruesome demise. As his foresight was never wrong, he did not want to see All Might's death. From there, they had a fight and separated.

Their falling out had left a sour taste for All Might, as afterwards he felt rather awkward with the idea of meeting his former partner and sidekick again.

However, according to Mirio Togata, Nighteye doesn't seem to hold any resentment or ill-will against All Might after their separation and consequent break-up. It is evident that Nighteye still admires and cares for All Might despite their disagreements. It is possible their falling out also left a sour taste for Nighteye as he had not seen him again afterward.

Nighteye is said to be always watching All Might's videos. He is also an avid collector of All Might-themed memorabilia as well very knowledgeable of his actions.

The two truly reconcile during Nighteye's final moments, when Nighteye passes and All-Might is left deeply saddened.

Mirio Togata
Mirio has been working under Nighteye for his internship for at least a year. Nighteye is the one who managed to improve Mirio's abilities and turn him into the number one student at U.A. High School. Much like Nezu, Nighteye believes Mirio is a worthy successor to All Might and One For All due to their similar charismatic personalities.

At first, Sir Nighteye only saw Mirio as the most suitable candidate to replace All Might, but during the time he was training him for that role, he learned that Mirio holds a deep respect and admiration for him and understands his behaviour, becoming his most treasured student. During Nighteye's final moments, Mirio rushes into the room to plea to him to hold on to teach him more. Nighteye comforts Mirio by using his Quirk one final time, assuring him he will be a great hero.

Izuku Midoriya
Being a major fan of All Might, Nighteye has a lot in common with Izuku. They're both able to hold long conversations about All Might's past achievements.

Despite this, Nighteye doesn’t hold Izuku in high regard and refuses to acknowledge him as the inheritor of One For All. However, Nighteye is impressed by Izuku’s field awareness, as during their short fight, Izuku is careful not to destroy any of Nighteye’s All Might possessions. The hero does state that he hired Izuku to work under his internship only to prove to the boy that he is unfit to be the inheritor of One for All, and initially plans to put Izuku through many hardships.

In a conversation with Gran Torino, Sir Nighteye does comment that Izuku is similar to All Might with the fact that they both possess similar heroic resolves, suggesting that he does recognize Izuku's potential and respect him.

During his final moments, he admits that Izuku is worthy of One for All. Izuku is deeply saddened when Nighteye passes away from his injuries.

Gran Torino
Since he knew about One For All and was All Might's sidekick, Nighteye was acquainted with All Might's mentor. Nighteye appears to be familiar with Gran Torino enough to perceive his signature erratic jumping that Izuku copied in his bout with him.

Gran Torino was present during All Might and Nighteye's falling out. He decides to use Izuku as a means of mediating the relationship between the two, showing he cares about Nighteye.

Bubble Girl
She is Nighteye's sidekick and is the one who would report any new information to him. She holds fear towards Nighteye if she fails to perform her tasks by his humorous standards.

Centipeder
He is Nighteye's affiliated office's sidekick and has helped with tracking and observing the Kai Chisaki investigation set forth by Nighteye's instructions. Centipeder does whatever Nighteye puts forth for him to do.