well, use some of the side, or secondary charecters for refrence.
like, Asui, she had a sad backstory, a funny and cool quirk, so u could use that.
or Todoroki, sad backstory, cool quirk.
everyone has a sad backstory.
except for Bakugo, really
so, sad backstories.
Iida's brother, Deku's dad, they have family issues
Todoroki, Kirishima, Shigaraki (not hero, but still) they all had bullying/abuse trauma
see the theme?
sad backstories kill.
also, for quirks, look at the elements, and look at charecters.
Todoroki, ice and fire, Kirishima, earth, Kaminari, lightning.
so, you could always look at that for inspo
or, like Aizawa, aka Eraser Head, just plain awesome!!!
let your creativity run wild!!!!!
also, even if its as simple as night vision, shape shifting, or breathing underwater, its cool!!!
hope i helped!!! :D