Limiter



...No matter how much effort one puts in, every living being has an intrinsic limit to its growth. Too much power becomes unbearable and overwhelms its host, turning it into a mindless rampaging monster. To ensure that we do not enter the realm where we lose all purpose and ability to reason, God has set limits to the growth of every being. The mechanism with which growth is controlled is called the limiter. A limiter (リミッター, Rimittā) is a term coined by Dr. Genus for his theory on explaining Saitama's strength, which defies common sense. No matter how much effort is put in, there will eventually be a point where a being stops growing. According to the theory, this growth limitation is placed on every being by God so they do not acquire so much power that they cannot control or handle it; furthermore, it is possible for this limit to be removed somehow and an individual can achieve heights far greater than what should be possible.

The knowledge of limiter is only known by Genus and Zombieman.

Removing the Limiter
In rare instances, it is possible for certain individuals to remove their limiters. Genus claims that this requires certain conditions. Becoming a Mysterious Being is not the same as removing one's limiter: It is a mutation triggered by negative emotions, experimentation, or the injection of Monster Cells, and the individual is reborn as a new being with a new limiter. Abnormally powerful humans such as the heroes always had the potential to become extraordinarily strong, and those who modify their bodies must modify again in order to improve beyond their natural limitations; they also have not broken their limiters. So far, there is only one confirmed individual who has managed to accomplish this feat: Saitama. Saitama was an ordinary person with no talents or potential, but through effort alone, he evolved beyond his limits and achieved power that Genus is unable to even fathom.

Garou, another individual, had potentially removed his limiter during the showdown between the Hero and Monster Associations. It is stated that "Garou's limiter [...] seems to be breaking!" and he was shown signs of that, such as rapid growth throughout his battles. When he punched Golden Sperm, the latter remarked that Garou's punch was many levels higher than what humans are normally capable of. In the end, however, he began running out of fumes and lost the power he had gained. Whether this means that he had failed to completely remove his limiter, or that he did but the limiter was placed back on, remains unclear.

There appears that there are side effects for removing one's limiter: Saitama lost his hair until he eventually became bald. As for Garou, when he was breaking his limiter, he mentioned how his body felt light as if his "spirit" was removed from his body; he was also transforming into a Mysterious Being.

Trivia

 * It is possible that the "God" Dr. Genus refers to is the same being that Homeless Emperor calls God.
 * Garou's side effect for breaking his limiter is possibly a Mysterious Being mutation; however, it appears to be different somehow. Saitama didn't consider him to be an actual Mysterious Being, but rather just a human in a monster costume. Though the costume claim was false, unlike any Mysterious Being so far, Garou's transformation managed to revert. Saitama is also very aware that humans are capable of turning into Mysterious Beings, so the fact that he saw Garou as a human after seeing his monster form hints a possible difference between Garou's transformation and an actual Mysterious Being transformation.
 * Gyoro Gyoro claims to know of a secret trick that turned a regular human into the Monster King, Orochi. She attempted to do it again to Garou by sending a bloodthirsty Royal Ripper and Bug God to tail him, knowing that they will fight him to the brink of death; those same conditions are what enabled Garou to break his limiter. Furthermore, just like Orochi, Garou also transformed into a immensely powerful monster that dwarfs even Dragon level monsters. This implies that there is a connection between Gyoro Gyoro, Orochi, Mysterious Beings, and the limiter.