I believe in this particular case you would put the Futanari tag down. While in this particular work it might be a guy, at the same time there is nothing hinting to that in this picture. Further more, this is a Female character. As such, the image itself would be Futanari.
This is a book about CJD, コスプレ女装男子 = cosplay cross-dressing boys. There is not futanari here, and in fact these are supposed to be original characters merely crossdressed as Touhou characters.
