More examples: #620559 | InCha no K Cup-chan 4 | 16,963 page 33 #376136 | Futari Asobi | 72,311 page 25

More examples: #545896 | Soshite Kyou mo Moteasobareru | 20,484 page 44 #632916 | Kare to Watashi no Kowareta Kizuna ~Kim… | 2,278 page 46 #573375 | Bare nakya Ii to Omotteta ~Daikirai na… | 4,054 page 20

I agree most 'hidden sex' tends to involve with 'hold the moan', but there are scenarios where the activity is not hidden. - sex/fellatio while on the phone - sex next to someone unconscious/asleep - 'hidden toy' in public, desperately holding back from moaning 'hidden sex' also doesn't have to involve with holding back moaning.

yeah, but doesn't this happen in most "hidden sex" scenarios?

This is related to 'hidden sex' and 'public sex', but the context is "not let others find out" by holding back moaning, such as in a phone call, or chatting with friend on balcony. Examples #146595 | Kono, Hikyoumono!! | Y- You Damn Coward! | 112,062 page 22 (behind curtain), page 26 (on the phone) #234167 | Junai Lyricism - True Love Lyricism | 19,962 page 169 (fingered in car), page 185 (fellatio'd in car)