[FJIN-162] Nude model: The ED husband who failed at trying to conceive confesses his cuckold fetish to his wife. Confused but willing for the sake of her loving husband, the wife gets turned on and drips love juice for a handsome model… Kokoro Ayase.

Um,

Although I’ve got a general idea of what you likely mean by “sneaky” sex, and I think I liked watching it,

I’m not really sure.

So – In the Nagae Style movie

[NSPS-828] To verify whether a beloved wife is a cuckold I let my wife become a nude model… Nao Yuuki

/?s=NSPS-828

There’s some pretty sneaky reaching around. . .

In

[HMN-592] My wife who was made to wear extreme land uniforms… After a struggle between shame and pleasure, I allowed her to be inseminated by a stranger… Itsukaichi Mei

/?s=HMN-592

The touchy-feely stuff also seemed pretty sneaky

But I remember seeing comments like that mostly in the movies from the Prestige DOCP Memorial Nude Photo Sessions

/series/絶倫チ○ポ男と素肌密着偽撮影会で寝取られ検証/

Care to elaborate of what you mean?