Mirai Sasaki

Sir Nighteye (サー・ナイトアイ) is a Pro Hero and Mirio Toogata's mentor. He is also a former sidekick of All Might.

Appearance
Sir Nighteye is a lean man with a well-kept appearance, wearing regular office clothes while on duty. He wears glasses and appears to be always glaring.

Personality
Sir Nighteye maintains a stoic and intimidating presence, with a cold and sharp glare, but that's only the side he shows in public. Nighteye actually greatly values humor and requires people to actually make him laugh first in order to acknowledge them. Nighteye believes that humor and energy are vital elements for the future of society and will punish subordinates that fail to display those qualities.

Nighteye is a big fan of All Might, watching videos about his deeds and keeping several of his collectibles. He is easily able to recollect events and details of All Might's heroism from the past. All Might also shaped Nighteye's vision of what a hero is supposed to represent: someone who instills fear on the heart of villains through power and hope on the hearts of civilians through good humor.

Though he can appear to be cold in some situations, he is very quick to jump to the defence of his sidekicks and anyone working under him. He is quick and very open about when he makes mistakes, and will defend other people who have made mistakes under his orders.

Unusually for a pro hero, Nighteye appears to prefer plain office clothes instead of an elaborate hero costume.

History
Sir Nighteye was once All Might's sidekick, however, they went through a fall out at some point in the past, and thus stopped working together.

After that, Nighteye started his own hero career, opening his own Hero Office. Mirio Togata would devote himself in training under him for a whole year.

Synopsis
Sir Nighteye was first mentioned by Mirio and Gran Torino as a potential mentor for Izuku

Sir Nighteye is first seen working on his computer in a dark room and being informed by Bubble Girl about the meeting between the League of Villains and Overhaul, the latter who is under investigation by Sir's organization.

Quirk and Abilities
Foresight (予知): Sir Nighteye's Quirk activates by first touching a target and then making eye contact with them. Once these conditions have been met, Sir Nighteye gains the ability to see the entirety of the targets future, second by second, for one whole hour. Sir Nighteye sees the future like frames of a film, and can only see the target from a third-person perspective and sometimes their surroundings. Sir Nighteye can only activate his Quirk once per 24 hours and has been shown that the future he sees are 100% accurate.

Physical Abilities: According to All Might, Sir Nighteye does not have any impressive physical abilities and acted more of a support with his intelligence.

Keen Intellect: Aside from his Quirk, Nighteye's strength lies with his intellect. He acted as the brains for All Might during their partnership. Nighteye uses his intelligence to come up with strategies to tackle situations and make sure the best outcome can be achieved.

Teaching Skills: Sir Nighteye's Hero tutoring skills are notable, as he managed to convert the then underachieving Mirio Togata into a powerful hero student in less than a year.

All Might
Nighteye is 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, Toshinori refused because of his rule to not take 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 Sensei and Nighteye pleaded All Might to retire and find a successor with similar traits as All Might. 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 sidekick's advice.

During their conflict, Nighteye brought up a future he saw of All Might via his '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 is never wrong, he did not want to see All Might's die. From there, they had a fight and separated.

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

However, according to Mirio, Nighteye doesn't seem to hold any resentment or ill-will against All Might after their separation. 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 to Nighteye as he has not seen him again afterwards.

Nighteye is said to be always watching All Might's videos. He is also an avid collector of All Might-themed products.

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

Mirio Toogata
Mirio had been working under Nighteye for his internship for at least one year. Nighteye is the one who managed to improve Mirio's abilities and turn him into the number one student at U.A.

Much like Nedzu, Nighteye believes Mirio is a worthy successor to All Might and One For All due to their similar charismatic personalities.

Mirio holds a deep respect for Nighteye and understands his mentor's behavior.

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. Nighteye even stated that he hired Izuku to work under his internship only to prove to the boy that he was a unfit to be the inheritor of One for All, and planned to put Izuku through many hardships.

In a conversation with Gran Torino, Sir Nighteye did 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.

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

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

Trivia

 * Nighteye's name and character could possibly be inspired by the DC Hero Dick Grayson, who was the sidekick of Batman under the name Robin before parting ways with his mentor and donning his own hero name, Nightwing.
 * Nighteye's requirement to have people make him laugh at least once resembles the character North Kaio from the Dragon Ball series.
 * Coincidentally, Nighteye's sidekick, Bubble Girl, has a similar name to the Dragon Ball character Bubbles, a monkey who lives with the Kaio.