Who is she or what is it from?

Kuro No Rider (黒のライダー) AKA Astolfo
https://myanimelist.net/character/79995/Kuro_no_Rider
from the Anime Fate/Apocrypha. It's a he not a she.
https://myanimelist.net/anime/34662/Fate_Apocrypha
In case u want more
https://luscious.net/albums/my_astolfo_collection_314257/

Kuro No Rider (黒のライダー) AKA Astolfo
https://myanimelist.net/character/79995/Kuro_no_Rider
from the Anime Fate/Apocrypha. It's a he not a she.
https://myanimelist.net/anime/34662/Fate_Apocrypha
In case u want more
https://luscious.net/albums/my_astolfo_collection_314257/

It's a he my fallen friend

i guess is Astolfo from Fate Series
He appears in Fate/Apocrypha
But is a trap...sorry friend

But the Fate-verse have a lot of others good waifus for you...and a lot of doujinshi