Mirai Sasaki, also known as Sir Nighteye was a Pro Hero and Mirio Togata's mentor. He was also formerly a sidekick and was considered to be the brains behind All Might. Sir Nighteye was a tall, lean-but-muscular man with rather sharp and elongated features. His shiny hair was always worn smoothed down and parted to his left, and was of a dark green color, with three yellow streaks towards the front, two on his right, and one on his left. His eyebrows were also yellowish, matching the rims of the triangular glasses he wore and the strikingly bright-yellow irises of his stern-looking eyes. His looks gave off a sense of authority and power, as he rarely smiled and looks stern, and he always appeared to be glaring. Unusually for a Pro Hero, Nighteye appeared to prefer plain office clothes (a plain white suit with gold buttons, a white dress shirt, and a red tie with white dots) instead of an elaborate hero costume. His clothes, however, seemed to be quite durable, as he used them during battles and they didn't show any sign of damage or tearing. Nighteye was designed with the intention of invoking the stereotypical image of a Japanese man. Sir Nighteye maintained a stoic and intimidating presence, with a cold and sharp glare, but that was only the side of his personality that he showed in public. Even with his supposedly cruel and intimidating stare, Nighteye greatly valued humor and actually required people to make him laugh before he acknowledged them. Nighteye believed that humor and energy were vital elements for the future of society and punished subordinates that failed to display those qualities. Nighteye was a big fan of All Might, having watched videos about his deeds and keeping many of his collectibles and merchandise. He was easily able to recollect events and details of All Might's heroism from the past, and his knowledge regarding All Might even came on par with that of Izuku Midoriya's. All Might also attempted to shape Nighteye's vision of what a hero was supposed to represent: someone who instills fear in the heart of villains through power and hope in the hearts of civilians through good humor. At the same time, Nighteye strongly cared for All Might and expressed grave concern when he would continue with his hero duties after receiving horrific injuries from his first battle with All For One. He pleaded with All Might to retire and focus on finding a successor, foreseeing that he would meet a horrible death should he continue serving as the Symbol of Peace. Despite this, Nighteye strongly disapproved of All Might choosing a Quirkless Izuku Midoriya to be his successor and inherit One For All. He protested against this strongly, saying that there would be any number of people more suitable and declared that Izuku could not become his successor on good intentions and willpower alone, showing a far more pragmatic approach. This would lead to their falling out and Nighteye focusing on finding a more worthy candidate, despite All Might having made his decision. Though he appeared to be rather 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. Sir Nighteye also had a pronounced conscience, as he regretted taking on Mirio Togata as his protégé and only seeing him as a suitable vessel for One For All at first, expressing how Mirio grew from that and went on to become his pride and joy. Nighteye had shown to fear using his Quirk to a large extent, particularly when it involved foreseeing an individual's future death, as he formerly believed that once he saw into the future, that future was set in motion and could not be changed, a mindset he changed shortly before his death when he witnessed Izuku Midoriya defying his Quirk's vision during the Shie Hassaikai Raid. Moments before he passed away, Nighteye smiled and encouraged those around him to do the same, saying that a world without smiles and humor has no bright future.