After too much thinking, massages.

The question short-circuited me or smth, decisions about such important things are hard!
One of my biggest & most fail-safe kinks is somnophilia, but if it was infinite amounts I would want to pick smth both parties are awake for I think, haha...

So, massages maybe, because
1) it fits their canon, ofc
2) I love the intimacy of intense physical touch
3) you can go a LOT of different ways with massages!

It's such a versatile trope, it can be undoubtedly hot but it can also be soft at the same time, or it can be frustrating and who doesn't love unresolved sexual tension.
It can have focus on your favorite area wherever it may be, so body worship etc kinks are easy to blend in.
It has a nice predetermined dynamic of giver/receiver & you can do a lot with that too, be it in a caring direction or in a darker one.
And it focusses on Reigen's hands. And man, do I love hands & Reigen's are pretty far on top of the list...

I've loved & wrote massages before RM, so I felt instantly blessed with Reigen's scams...