OK i think the NTR tag does qualify for Kazuku Airi story. using the wiki definition "Description: Another person's spouse / partner being unfaithful and the one being cuckolded being aware of the situation. Also acceptable for when the story is clearly meant to invoke jealousy or sympathy on behalf of the person being cuckolded." her real boyfriend knows his doppelganger is out to bang his girlfriend. the girlfriend doesn't know she is having sex with someone else technically. i think the reader is a subject of jealousy and can qualify.