UPDATE ON THE QUIRK THING:
I found it. The coolest not Original but not from MHA "quirk".
Sett's Haymaker Ability from League of Legends. It basically boils down to the more hits I take, the harder I hit back. At max energy, he has the potential to one shot people he targets. Here's what I have down for Haymaker(renamed Showstopper because Haymaker sounds boring)
Showstopper
What it does: The more damage the user takes, the more energy is stored up. Depending on the amount of energy stored, the user can reflect all of the energy stored multiplied by 4 in a single punch. During this punch, they are invulnerable. This quirk also makes the user many times more naturally resilient than a normal human. E.g The user is able to survive a hit from a speeding car at 120 mph, albeit with broken bones and severe internal injuries. Resilience can be increased with training and use. Pain is not affected by the quirk, so getting hit by the car would still feel like you were dying. There is no limit to energy stored. The user will glow gold when the stored energy is able to level a small building
Drawbacks: The user’s constitution must be incredibly tough, or they will pass out before they reach their maximum power. This means if they can’t deal with pain, they won’t be able to stay conscious long enough to use their quirk. If the user stops absorbing energy, then they will begin to lose the energy over a period of 15 seconds, 5 seconds after they’ve stopped taking hits.
Creative uses: the user may simply tank hits until they reach the desired energy capacity and fire. This is not recommended. Painkillers are a must if the user wishes to unleash a punch beyond their pain limit.
This is probably going to the the quirk that I use for a potential MHA fic.