Mirai Sasaki

Sir Nighteye (サー・ナイトアイ) was a Pro Hero and Mirio Togata's mentor. He was also a former Sidekick and the brains of All Might. Sir Nighteye was famous for being one of the smartest people in the world until his death after the raid on the Shie Hassaikai.

Appearance
Sir Nighteye was a lean, but muscular man with a clean, well-kept appearance, wearing regular office clothes (a light gray suit with a red polka-dotted tie) while on duty. He wore a pair of glasses and appeared to be always glaring. His hair was of a dark greenish color, save for a few blond strands located on his bangs as well as blond eyebrows.

Unusually for a Pro Hero, Nighteye appeared to prefer plain office clothes instead of an elaborate Hero costume. His clothes, however, seem to be quite durable as he used them during battles and they didn't show any sign of damage or tearing.

According to his character bio in Volume 14, Nighteye was designed with the intention of invoking the stereotypical image of a Japanese man.

Personality
Sir Nighteye maintained a stoic and intimidating presence, with a cold and sharp glare, but that was only the side he showed in public. Nighteye actually greatly valued humor and required people to actually make him laugh first in order to acknowledge them. Nighteye believed that humor and energy are vital elements for the future of society and punished subordinates that failed to display those qualities.

Nighteye was a big fan of All Might, watching videos about his deeds and keeping several of his collectibles. He was 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 in the heart of villains through power and hope in the hearts of civilians through good humor.

Though he appeared to be cold in some situations, he was very quick to jump to the defense of his sidekicks and anyone who worked under him. He was quick and very open about when he made mistakes and defended other people who had made mistakes under his orders.

It appears that Nighteye feared using his Quirk to a large extent, particularly when it involves foreseeing an individual's future death as he formerly believed that once he saw into the future that future is set in motion and cannot be changed, a mindset he changed shortly before his death when he witnessed Midoriya defying his quirk's vision during the Shie Hassaikai arc.

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 to training under him for a whole year.

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

He was 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 was under investigation by Sir's organization. He ends up mentoring Izuku, but before he gets hired he has to pass his test. What Izuku needs to do is to get the stamp out of Sir Nighteye's hand and stamp the page.

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 target's 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 is 100% accurate. However recent events seem to suggest that quirks that alter time in some way can affect the accuracy of his quirk, possibly rendering the predicted outcomes moot, and/or void.

Physical Abilities: According to All Might, Sir Nighteye does not have any impressive physical abilities and acted more of a support for his intelligence. However he is shown to be exceptionally fast and capable of throwing heavy projectiles as well as being able trip up very large foes. Furthermore under his suit he sports an impressive physique showing that either he deliberately hides his physical prowess to catch opponents off-guard, or he is simply underestimated by most.

Genius-Level 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.

Equipment & Weapons
Super Density Stamp Seals: Sir Nighteye's preferred weapon; special seals that weigh 5 kilograms (11 pounds) each. He can throw those objects with great force and accuracy. He wields those due to a humorous perception of what kind of weapon would best suit a salaryman.

Battles
Izuku Midoriya, Mirio Togata, & Sir Nighteye vs. Kai Chisaki: Win

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, 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 partner'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 was 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 partner and sidekick again.

However, according to Mirio, 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 to Nighteye as he has 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 products.

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

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

Mirio Togata
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 Nezu, 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. During Nighteye's final moments - he comforts Mirio by using his Quirk one final time.

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 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.

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 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.

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

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 Kaioh from the Dragon Ball series.
 * Coincidentally, Nighteye's sidekick, Bubble Girl, has a similar name to the Dragon Ball character Bubbles, the pet monkey of Kaioh.
 * Nighteye appears to be a fan of Preyure (a reference to the anime series Precure).
 * It is mentioned that he took care of All Might's file work before their falling out.
 * Nighteye is the first major hero in the series to die.