Energy Suck

Vitality Stealing (をう) is a Quirk used by Rikiya Katsukame.

Description
By making physical contact and inhaling, Rikiya can absorb the vitality of others, making himself bigger and stronger.

This Quirk has the double advantage of strengthening Rikiya while simultaneously weakening his foes. Under the effect of Trigger, Rikiya can absorb the vitality of nearby people only by inhaling, no longer requiring contact. In the latter case, the Quirk activated entirely on its own while he was unconscious as soon as the drug took effect, waking him up and replenishing his stamina. This allowed him to fight evenly against Ryuko Tatsuma, the No. 9 Pro Hero; Nejire Hado, one of The Big 3 of U.A. High School and several other Pro Heroes, policemen, and interns for 20 minutes.

It was only when the effects of the drug wore off that the weakened heroes from Ryuku's office were able to defeat him with a combined attack. By contrast, before he took the drug, Rikiya had been quickly subdued by Ryuko alone.

Trivia

 * Rikiya's Quirk seems to be heavily based on the powers of Superman villain Parasite, who could also absorb the strength and energy of others through touch in order to add to his own temporarily.