Overclock

Overclock (オーバークロック) was the Quirk used previously by Iwao Oguro, until it was stolen from him by All For One. All For One eventually gave this Quirk to Number 6.

Description
Overclock allows the user to accelerate to extreme speeds, to the point that to the user, it looks like nothing is moving. According to Iwao, its true ability consists of stimulating the brain, speeding up the user's perception and thoughts relative to everything else, allowing them to move at a much faster speed than others.

In normal situations, the user can move at speeds approximately three to ten times faster than normal. In emergency situations, when the user's fight or flight response is active, the user can move at speeds a few dozen times faster than normal. The user can move fast enough to outpace bullets. The user can move fast enough to the point that the world seems completely frozen.

Overclock also grants the user heightened senses, allowing them to see, hear, and think at hyper speed. They're able to clearly hear words that have been sped up to three-hundred times the normal speed when the Quirk is active.

Combining it with his healing factor, the villain Number 6 can use Overclock to promote cell growth, allowing him to heal grievous injuries much faster. As he has parasitic cells in his body, he can also accelerate their growth as well, allowing them to merge with parts of his body, if he so wishes, even being able to grow a new limb out of the merged cells.

The heightened senses granted from Overclock can give the user the ability to read a person's subconscious reactions to both manipulate and react to a person's reactions without the subject even knowing.

Weaknesses
Overclock has several drawbacks. Due to it depriving its user of oxygen, it has a necessary cool-down period between uses, and can only be used for a few seconds at most.

Iwao states that access to the Quirk can be sealed off if the user's brain is deprived of oxygen, and if the user has a serious brain injury, such as a concussion. If the user is intensely focused on something, the user experiences a sort of "brain drain", which reduces the amount of time they can actively use the Quirk. If the user remains too focused while using their Quirk, they can also risk depriving their brain of oxygen, sealing off access to the Quirk. Iwao also implies that extensive physical injury, not just on the head, would be enough to seal access to the Quirk.

If the user is knocked into the air, the acceleration aspect of the Quirk becomes useless.

Number 6 eventually developed the Hi-Crawler transformation, which nullified all of Overclock's weaknesses when in use.

Trivia

 * Overclock refers to the term used when running a computer's processor higher than the recommended speed to achieve greater results. In this case, the "computer" refers to the user's body and the "processor" refers to their brain.
 * The abilities of Overclock, alongside the Hero Costumes and designs of Number 6 and O'Clock, appear very similar to those of DC's The Flash and the other speedsters. This reference can also be attributed to the lightning generated when utilizing the Quirk.
 * The concept of accelerating at the point that it looks like nothing is moving can resemble Quicksilver's ability to move at extreme speeds as shown in the 2016 movie, X-Men: Apocalypse.