Cell Activation allows its user to activate the cells in their body or another person's body through touch. This increases regeneration, recovery time, and can even improve physical condition.
This Quirk drains the user's stamina when activated, and continued usage can cause fatigue. The Quirk also can't be activated on certain people depending on their blood type.
Katsuma is able to activate and speed up the activity of cells in the body of anyone he touches, and it is implied he can use it on himself.
This Quirk was used on Izuku and Katsuki after their first battle with Nine, and Katsuma was able to heal their wounds, speed up their recovery, and improve their physical performance. After prolonged usage during that treatment, Katsuma became exhausted. So far, his Quirk has been shown to work on people with Type O, A, and B blood.
Katsuma's father is able to activate the cells in his own body or another person's body and is able to heal wounds and speed up recovery time.
He stated that the Quirk can only be used on those with Type A blood.
Nine stole this Quirk from Katsuma's father but was unable to use it on himself due to the Quirk being incompatible on people with Type B blood.