Alright, this is a tricky one and feels like walking a tightrope, because what exactly qualifies as "top-rated" can be so subjective. Mainstream sites like Archive of Our Own (AO3) and FanFiction.net obviously have the most content, but their tagging and rating systems treat mature themes differently. AO3's 'Explicit' tag is where you'd look, and their kudos system can point to popular fics, but a lot of readers don't publicly kudo 'lemon' works even if they enjoy them, so the ratings can be misleading.
For that specific pairing, it's such a niche ship that the volume isn't huge anywhere. You might find dedicated, well-written pieces scattered, but they're rarely the most kudo'd or reviewed fics in the entire fandom. I've stumbled on some surprisingly good ones on smaller, now-defunct personal archives or LiveJournal communities that people have mirrored on AO3. The search is honestly half the battle; using the right combination of tags like 'Naruto/Kurenai Yuhi', 'Explicit', and maybe 'Alternate Universe' on AO3 is your best starting point.
Honestly, sometimes the 'top-rated' fics aren't the most enjoyable—they're just the ones that got there first or had a catchy summary. For something this specific, I'd sort by date updated and read a few recent ones that have decent prose in the first paragraph. The quality can be wildly inconsistent.