That Time When I, an Exorcist, Lost to Futanari Demon Cock

Our protagonist, an exorcist, ventures to investigate the alleged possessed painting. Turns out it really was possessed, and by an immensely powerful succubus to boot. The moment he sees her, he realizes she’s way out of his league. Made prisoner, he can only struggle in vain, as the futanari succubus ravages his body and slowly turns him in one of her own kind...

(Source: Fakku!)