Accelerated Development

Accelerated Development is the ability to raise one's strength, skills and abilities at an extreme rate.

Overview
The user can grow far stronger through fighting and training, improving their natural abilities far faster than most other characters.

For instance, nearly a year into his training regiment, Saitama noted that as a result of his repetitive routine, his body had adapted to "[moving] like a hero should", and his power began to explode at a rapid rate. In no time at all, he reached unparalleled levels of strength, speed, and durability through this regiment, a testament to his growth rate; however, according to Genos, Saitama himself cannot explain the secret behind his own strength, and the cyborg believes that he should not have become that unbelievably powerful with only that level of training.

Garou's usage of this ability is also at an incredible degree, as he quickly gets stronger after each battle. His usage of this ability is enhanced even further after his transformation into a half-monster, going from having difficulty against Royal Ripper to being capable of defeating the latter effortlessly. During his fight with Orochi, Garou has shown to become faster the longer he fought, only being subdued when the Monster King decided to quickly knock him unconscious without giving him the chance to evolve further.

When fighting Superalloy Darkshine, an extremely powerful S-Class hero known for his remarkable strength and overwhelming durability, Garou initially could not even injure the hero and had difficulty keeping up with his strength. However; as their fight went on, noted by Darkshine himself, Garou continuously became stronger and faster after every single time he was beaten, as well as being able to further improve his fighting skills and techniques in the middle of the fight, allowing him to completely overwhelm the hero.

Trivia

 * Although Garou's usage of this ability is similar to that of Metal Bat's Fighting Spirit, in his case however, Garou's boosts are permanent whereas Metal Bat's are only temporary.