Brainwashing allows Hitoshi to assume control of anyone who responds to one of his statements, forcing them to do as he says.
Brainwashing is willingly activated by Hitoshi, who otherwise can hold normal conversations with other people without having to brainwash them. It is shown that he can control more than one person at once, but this has to be done individually, as brainwashing multiple targets simultaneously is beyond Hitoshi's capabilities. He needs to concentrate on his desired target in order to activate his Quirk.
Victims feel dazed when being controlled, but will remain largely aware of their current state of being brainwashed, despite looking completely spaced out. They are rendered essentially caged in their own bodies and feeling helpless all the time until the brainwashing effect breaks. Those who end up brainwashed will be forced to follow all of Hitoshi's commands.
Hitoshi is unable to have his brainwashed targets perform orders that require complex brain activity, such as thinking or talking, so he must keep his commands simple for them to be followed.
The brainwashing effect requires the target to answer to take place, therefore, as long as the target remains silent, this Quirk will not have any effect on them. It is also possible to escape the mind control if the victim is hit by a sufficiently strong physical jolt or through a similar amount of pain.
Brainwashing is implied to not work on non-living entities, which can justify Hitoshi's failure in the U.A. Entrance Exam (as the targets in the practical portion of the exam were robots). Using electronic devices to transmit or enhance Hitoshi's voice (by converting it into an electric signal) will make the Quirk lose its effect.
Despite its tremendous potential, Hitoshi has always thought of his Quirk as troublesome. Due to its nature, it wasn't effective against the Villain Bots of the U.A. Entrance Exam, meaning that Hitoshi had little chance of passing the test. Its conditions and effects also made people wary of Hitoshi, as they believed Brainwashing suited someone with a villainous personality.
Brainwashing is most effective when used as a first strike, assuming the opponent doesn't know about the Quirk's conditions beforehand. As such, Hitoshi makes sure to casually strike a conversation with an unsuspecting target, taking control the moment they reply to him. If the foe is somehow already aware of Brainwashing's process, Hitoshi is still capable of taunting or relying on some other form of trickery to force them to respond.
At some time before the Joint Training Arc, Hitoshi received a new piece of equipment: Artificial Vocal Cords, a mask-like device that allows Hitoshi to alter the tone of his voice through non-electronic mechanisms. Through this item, Hitoshi can easily trick opponents into submission, pretending to be someone else through vocal mimicry.
People that have been brainwashed by Hitoshi include:
- Mashirao Ojiro
- Yuga Aoyama
- Nirengeki Shoda
- Tetsutetsu Tetsutetsu
- Izuku Midoriya
- Jurota Shishida
- Ibara Shiozaki
- Several unnamed students of the Obstacle Race
- Artificial Vocal Cords: Persona Chords: By using his Artificial Vocal Cords equipment, Hitoshi can modify his vocal tone in order to mimic other people's voices, tricking enemies into answering him and setting them up to the effects of his Brainwashing.
- Brainwashing - Wikipedia article about the concept Hitoshi's Quirk revolves around.