He’s a tough person to impress who ultimately comes around. Why did Nighteye accept Deku?
Nighteye chooses to accept Deku because he destroys no All Might memorabilia during the “steal the seal” challenge. Impressed with his focus and ability to concoct a plan, Nighteye accepts Deku despite not completing the challenge.
Deku also theorizes that Nighteye is partially accepting him because he hopes Deku will give the quirk up to Mirio.
Nighteye decides to accept Deku
In chapter #128, Deku tries to prove himself to Nighteye. Off the strength of Mirio’s recommendation, Deku is attempting to gain Nighteye’s approval in order to have a work-study under the pro hero’s agency. The first time students had to work with pros, Deku didn’t get any offers.
Sir Nighteye’s quirk is “Foresight.” This allows him to see any move that his target will make in advance for the next hour so long as he makes physical contact and locks eye contact. The Pro Hero says that if Deku can steal the seal from him, he can stamp the approval letter for himself.
Nighteye calls Deku an inferior version of Gran Torino as he zooms around the room. There’s only a small amount of time that Deku can steal the seal, and he has no major gameplan.
The pro continues to taunt Deku, saying it should have been Mirio who received All Might’s power. Nighteye says he doesn’t understand why All Might chose Deku.
Needing to distract Nighteye’s quirk, Deku throws books and papers in the air to create a distraction. The pro informs Deku that he can mess the room up as much as he wants during the challenge.
Eventually, the timer ends. Deku is unsuccessfully able to steal the seal from Nighteye.
Nighteye asks if Deku lost focus, but the boy disagrees. He says he did not want to step on All Might’s Tenth Anniversary Commemorative Poster that’s not sold anywhere.
The pro then takes notice that while moving around at Gran Torino’s speed, Deku is able to successfully avoid all the All Might merchandise surrounding the room. Despite Nighteye’s taunts clearly bothering Deku, he still manages to take note of his surroundings and concoct a plan.
Mirio then enters the room. Nighteye informs him that he’ll be accepting Deku, despite failing to steal the seal.
One For All can only be transferred when its wielder wills it, Deku explains. He then suggests that Nighteye accepts him in hopes that Deku will become frustrated and give the quirk up.
So that’s the answer. Nighteye chooses to accept Deku because he’s impressed by his precise movements during the “steal the seal” challenge. Deku destroys no All Might memorabilia during the challenge.