Is this not Nero? Looks extremely close to her if its just an OC. Good art anyways.
It definitely looks like Nero. I tried checking the artist's Skeb, but it looks like it was a private request, so couldn't use that to confirm. Maybe if they crosspost it to their pixiv they'll tag it as Nero or an OC.
Yeah I don't see any issues with tagging this as Nero. Not like anyone's going to question it unless there's info somewhere that says otherwise.
One of the replies on the Twitter post seems like it might be the requester, so you could try asking them, but for now I'm just going to tag it as Nero.