This is Nagi after she becomes corrupted. She was shown in that school uniform.
No idea if you'd just want to use tan + Nagi with this or make a specific tag. Visually the difference between this Nagi and the normal Nagi is skin color and the color of hairband/hair tubes (black instead of white).
According to what I see (no extra info apart from anime series ) and tags (one of them gave me a lot of pic with her) it's Nagi, but more tanned. Personally, I would wait until more arts with her come out and then make a special tag like corrupted_nagi_(kannagi) or something like that.
I expect more fanart of this variant of Nagi to appear, but I will hold my reservations on it ever achieving any significant numbers (at least for now). Fanart directly from manga tends to be slow and sometimes practically nonexistent. Everything that is here and being made is still mostly influenced by the anime.
Though I honestly do expect that some hentai doujins using this variant will pop up within a years time.
