This post discusses questionable adult content, mainly fiction and adult fiction based on real people and primarily adult fiction based on underaged real people. Consider yourself warned.
As users of the site may know, the Archive of Our Own is fairly open in terms of content and fandoms, so long as it's tagged properly.
This means that, yes, you are likely to find a lot of kinky stuff on the site, including things that you may fundamentally disagree with (content involving underage characters, or rape/non-consensual sex). With fictional characters this is generally not a problem - though problematic tags exist, this generally isn't hurting anyone, and it's allowed in AO3's terms.
It's come to my attention recently that 'real person fiction' or RPF - think all the stuff you wrote about the Game Grumps, or the Sanders Sides, etc - is treated the same as all other fiction on the site.
Which means, yes, explicit RPF exists. (Which I do find a little skeevy, but is again within AO3's terms.)
Please read through the post linked above, but: in short, it seems so long as it's tagged correctly, any fiction, regarding any person - real or fictional - is allowed. Including if the 'real person' is underaged.
So, after seeing and reading this exchange thanks to a fellow Splatoon fiction writer, I have to make the decision to no longer update Begin Again on AO3.
I have had some discussion on the Discord server trying to decide how I should proceed. Currently the plan is to simply continue updating the version on Fanfiction.net, but I think I would like to use the opportunity to set up an additional mirror of the fic. Ideally I'd like to have it be somewhere where people can discover it, but I'm also open to having it be available on this domain, going forward.
Nov 18 edit: This was written before I had set up this new site, so this additional mirror now exists: see the Writing link in the top navigation.