Down to the Bone: MHAxUndertale

Izuku was born with a fairly useless quirk, all it did was allow him to summon bones, these bones could not have done much, but when his father, All Might gives him the Power of One For All, his quirk is amplified, and he suddenly becomes one of the most powerful beings this planet has ever seen.

Note: I have never played Undertale, I just think Sans is cool, so don't expect much undertale story...