As fans must know, while My Hero Academia isn't devoid of deaths, its first major death was quite controversial. This is because Sir Nighteye, who was introduced in the Shie Hassaikai Arc, ended up dying in the same story arc, suggesting that he was only introduced to expose Deku to the "deceased mentor trope."
Despite how Kohei Horikoshi may have treated the character, one cannot deny that his introduction was worthwhile. The character not only gave Deku and Mirio a rejuvenated sense as heroes, but also foreshadowed the possible death of fan-favorite character All Might.
As evident from the manga's conclusion, Sir Nighteye was wrong about his foresight on All Might, but that wasn't the case for Mirio, who ended up just the way the hero foresaw using his Quirk.
Disclaimer: This article contains spoilers from the My Hero Academia manga.
Sir Nighteye's foresight on Mirio comes to fruition in My Hero Academia

As fans might remember, during the Shie Hassaikai Arc, it was revealed how Sir Nighteye had previously foreseen All Might's future after he was critically injured at the hands of All For One. As per what he saw, the No.1 Hero was going to die a gruesome death at the hands of a villain if he were to continue his career as a hero. Hence, Sir Nighteye asked All Might to retire, but unfortunately, the hero denied the request.
Nevertheless, as manga readers must know by now, All Might never passed away in the series. While there was a moment during the Final War Arc in which All For One came close to killing All Might, Katsuki Bakugo came to his rescue, helping him avoid his gruesome fate.

Such a development could convince fans that Sir Nighteye's foresight wasn't great for looking far into the future. However, Mirio Togata's endgame feat proved otherwise, as the former All Might sidekick's foresight was proven true in the manga's epilogue chapter.
As fans must remember, when Sir Nighteye was on his deathbed and Mirio wept in front of him, the hero raised his arm, touched his student's face, and used his Foresight Quirk for the last time. As fans must remember, Mirio Togata had lost his Quirk during the fight against Overhaul. Thus, he believed that his Hero career had come to an end.

Nevertheless, as foreseen by Sir Nighteye, Lemillion was going to be an outstanding hero in the future. Nighteye comforted his pupil and told him that his future should not change, no matter what.
While many fans believed that Sir Nighteye was only trying to comfort his student, as revealed by the manga's epilogue chapter, what he had foreseen was true. Years after regaining his Quirk and partaking in the final war, Mirio Togata was ranked No.1 in the Hero charts.
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