That's so sweet!! Love me some good doting,,,
I'd think it can only so nonsexual considering they'd both have to be naked - I mean it is their skin.

I can imagine Opal making some bs excuse that the skin on her cock is too sensitive or something and she needs somebody else (aka Bismuth) to do it. If course she'd act all flirty and try to get Bismuth as red in the face as possible...

But also the nonsexual side does sound really nice! Getting together and helping eachother out, the motherly/sonly affection and all!