Foresight grants Sir Nighteye the ability to accurately predict all of the target's future moves and actions for an entire hour.
Foresight activates by first touching a target and then making eye contact with them. Once these conditions have been met, Nighteye is capable of watching the target's future lifetime from a third-person perspective that showcases the target themselves and their immediate surroundings, in a manner similar to a flashback. Nighteye does not appear to have a limit to how much he is able to see into the future, being capable of foreseeing events that are years beyond present time.
One of the drawbacks to this ability is that Nighteye is incapable of giving a precise date to when said events will happen, thus having to rely on rough estimates; the events themselves still end up happening sooner or later due to the outcome shown in Nighteye's vision being apparently impossible to change, although this was proven to be false when Izuku Midoriya completely defied the vision seen during his fight against Kai Chisaki.
As the nature of Foresight is completely sight-based, Nighteye is unable to listen to future dialogue and thus cannot fully interpret certain actions and events. Breaking eye contact with Nighteye through any means will prevent him from further predicting opponent moves.
Once Foresight is activated, Nighteye requires a 24-hour interval before he is able to activate it again.
The conditions to activate Foresight are considered a company secret, presumably to keep potential opponents in the dark about Sir Nighteye's abilities.
In combat situations, assuming he managed to make physical contact with his opponent beforehand, Sir Nighteye used Foresight mostly for dodging purposes. Having knowledge of the enemy's each and every move coupled with his own experience and physical prowess, Nighteye could become virtually untouchable in battle as long as he maintained eye contact with whoever was facing him, regardless of how fast they were. Foresight was also extremely useful for investigative work, due to the amount of information one could attain about a target by just witnessing their future actions.
Sir Nighteye was extremely careful and reluctant about using his Quirk thanks to his fatalistic mindset, seemingly believing that all visualized outcomes, including negative ones, were fated to occur and would be impossible to impede. As such, he refused to employ Foresight for situations he couldn't foresee through normal means, using it solely as a way to ensure results that were already under his control and likely to happen in the first place.
The people Sir Nighteye was confirmed to have foreseen (as well as their respective fates, confirmed or not) include:
- All Might: Without All Might's consent, Sir Nighteye was able to envision him meeting a "horrifying demise" against an unspecified villain. All Might believes this prediction is still up and might happen in the following one or two years.
- Izuku Midoriya: As part of Izuku's test to work for his office, Sir Nighteye challenged the student to take a stamp from his hands, with Izuku being unaware of Foresight's activating conditions. Sir Nighteye was able to foresee all of Izuku's moves, which resulted in the latter failing his test, although Izuku would end up getting employed anyway (due to that being part of Sir's vision as well).
- Unnamed Shie Hassaikai member: During a shopping trip, Sir would stumble into a shady figure buying toys. Thinking of his behavior as suspicious, Sir approached the stranger and secretly used his Quirk on him, revealing the location Eri was being held.
- Kai Chisaki: While fighting the leader of the Shie Hassaikai, Sir briefly had an opportunity to activate his Quirk on him, coming across a future where Izuku Midoriya would get slaughtered by Kai. This future didn't come to pass, however, changing Sir's perspective about Foresight.
- Mirio Togata: On his death bed, Sir Nighteye used Foresight one last time on Mirio. While he didn't give off any specific details, he was glad to know that his pupil would become an "outstanding hero".
- Precognition - Wikipedia article about the concept behind Sir Nighteye's Quirk.