By making physical contact and inhaling, Rikiya can absorb the vitality of others, giving him more stamina while making himself bigger and stronger.
This Quirk has the advantage of strengthening Rikiya while simultaneously weakening his foes. Under the effect of Trigger, Rikiya can absorb the vitality of nearby people by only inhaling, no longer requiring contact. In the latter case, the Quirk activated entirely on it's 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. 10 Pro Hero (formerly No. 9), Nejire Hado, one of The Big 3 of U.A. High School, 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 Ryuko'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.
- 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.