This Quirk allows the user to detect any potential threats in the surrounding area, thus giving the user the opportunity to properly react to them quickly, similar to a sixth sense. The detection of a threat is described by Izuku as a sharp stabbing sensation in his head.
According to Izuku, this Quirk takes a large toll on the user's body depending on the threat it senses, although this may be a result of the Quirk being strengthened by One For All. This drawback doesn't seem to adversely affect Izuku anymore, implying that it can be made mild through training.
Sufficiently fast attacks can also prevent the user from being able to properly dodge them, as Izuku was heavily injured by Lady Nagant's bullet despite using Danger Sense.
If the user is in no actual danger, such as if their opponents have no true malice and are just trying to help, then the Quirk won't be triggered.
It is likely that Hikage used this Quirk in conjunction with One For All, though his fighting style with Danger Sense currently remains unknown.
During the Paranormal Liberation War, after Katsuki Bakugo was injured by Tomura Shigaraki, Deku snaps, manifesting the Quirk for the first time, although he would not be aware of it. Later, Izuku would feel the Danger Sense again when Gigantomachia was about to free himself from Best Jeanist's wires, but he would not understand the origin of that feeling. Then, after being momentarily knocked out by Dabi's flames, Izuku felt the sharp pain in his head again, finally understanding the reason for it.
He remembers the notes All Might had gathered about the previous One For All users and realizes he's awakened this Quirk. However, due to the Quirk's sudden awakening and his lack of training with Danger Sense, Izuku found it hard to stay conscious with the signals being sent to his brain, though he still forced himself to keep fighting.
During his hunt for the League of Villains, Izuku primarily uses this Quirk as a way to track down nearby criminals, sensing the sharp twinge in his head before heading off in the direction of the danger.
Izuku uses this Danger Sense more effectively in his battle with Muscular, using the Quirk and his previous fight with the villain to better dodge his attacks.
Izuku uses this Quirk again when attempting to flee from Lady Nagant's bullets, but even with the aid of Danger Sense, he's unable to fully evade the bullets and gets injured.
- Danger Sense could be a reference to the Marvel character Spider-Man's Spider-Sense which was also used to sense incoming danger.