Besides their color scheme, red eyes and white/grey hair, Eri and Tomura come from a pretty similar background.
Both of their quirks activated and accidentally, or maybe in Tomura’s case purposefully, killed their fathers.
Eri’s mother abandoned her and Tomura’s mother is never shown but either she abandoned him or maybe he killed her too.
Both were raised by people who didn’t care about their well-being and only wanted to use them for personal gain.
Eri and Tomura have been mentally warped by the people that raised them as well. Eri into thinking she deserves to be hurt and used. And Tomura into being nothing more than a puppet for All for Ones goals.
I think it’d be really nice if one day Eri and Tomura could both get the professional help they need to overcome years of neglect and abuse and maybe even bond over everything that’s happened to them.