There is no R-18 scenes in the regular version.
A member registered Mar 28, 2016 · View creator page →
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Devil Rhythm -Silver Phantom- R18 comments · Posted in Devil Rhythm -Silver Phantom- R18 comments
About purchasing, you need send a message to the staff of itch.io.
I don't know how their purchasing system works.
Another guy met the same problem recently.
I think there would be something itch.io could do for you.
At least they could tell you why.