User blog comment:Trident81/The Most Powerful Quirk/@comment-35975040-20180703093005

Definitely Overhaul. Since I don't know much about Eri's quirk at the moment, I'll discuss Overhaul instead.

The ability to deconstruct and reconstruct both biotic and abiotic things is just too insane of an ability. The capabilities of this quirk that I can cite from the top of my head are: shaping and reshaping terrain at will, disintegrating and reassembling a person to "repair" their injuries, instantaneously killing someone (Magne) on contact, deconstructing and reconstructing someone to restore their stamina, as well as literally fuse one person and another while being fully able to use the other person's quirk, if any.

If this guy went crazy and dumped his Yakuza methods to go on a rampage instead, it'll be too difficult to stop.

Compared to One for All, it's not "strong" combat-wise, but to be honest, One for All is as strong as it is because of the energy that has accumulated over time when it was cultivated by one person then passed to another. One for All also seems to need the host to be in peak condition to even survive the quirk, and Deku was only able to defeat Kaiju Overhaul when Eri continuously reset Deku's body.

The of this quirk that I remember is that it gives Chisaki rashes (?), it might be difficult to control, and it requires physical contact to be useful. But overall, it's pretty powerful.