In case anybody cares, this was a reference to Index's voice actress, Iguchi Yuka, singing a cover of "Only My Railgun" (the OP for the first season of To Aru Kagaku no Railgun).
Does anybody know whether these characters are from an existing work of some sort? I see the "original" tag, but they seem to have an ongoing story behind them that we see bits and pieces of in the posted art. OTOH, I can't find any mention of a "ricky barnes" on FFN or AO3, which hints that there isn't an existing fanfic about them (and I think fanfics don't get Copyright tags here).
This alternative Hoshino is called "Hoshino (Battle)", as unlike the regular Hoshino who is laid back, this Hoshino is more serious and uses her shield full time along with using both a shotgun and handgun.