The Japanese and Spanish R sound are effectively the same.

This is not about the Spanish rolling double R sound, this is about the single R.

So, I thought I was cheating the system… using my Japanese R sound in place of Spanish R's… but… they are literally the same. A Spanish friend told me the trick to learning RR sound was to just repeat "ara ara ara ara" until your tongue falls into place and does the thing…
uh. That is literally just Japanese "ara ara"

I have even heard the RRR trill in certain Japanese dialects. Anyway, if you're stupid like me and didn't connect the dots, being able to make that sound in one language is a jump start at pronouncing it in the other. The rolling version takes some work but you put your tongue in the same place.