RaedaX_1
Hey I was thinking for his resistance training maybe you could have the combined one just be called resist it would they him resist anything he could perceive with a mix of energy and will power I imagine it working like a shonin protagonist where he just forces his demonic energy to deny things like it envelopes him and then repulse fire or makeing it so when he eventually becomes able to reach the speed of light he can use his willpower to force reality to let him go faster. Now that I think about it demonic power is all about desires/Obsesion so he should be able to do that anyway But I think his high tier Resist should be able to resist concepts/the laws of physics through sheer willpower. Like low tier reality worping