In terms of what kinds of sexual acts they have performed, I don't think anyone will ever beat Ibuki Haruhi (春妃いぶき):
(She's also my avatar BTW.)
This girl's debut was a "losing her virginity" where the men literally r***ing her and shit on her. I assumed they had made up the part about her being a virgin, but they actually had her hold up a paper supposedly from a doctor verifying her virginity, and she did bleed a lot. Obviously that can be faked, but then I saw a later interview where she talked about it as her first experience, and what her life was like going up to that, and she sure did make it SOUND real.
She then did a whole bunch of videos with pretty much everything, ranging from scat to enema to puking. She also did a dog sex video, and even one that was basically her eating cockroaches and doing disgusting things with them.
She retired once then made a comeback as Aoi Yuki (優木あおい):
At first she seemed to e going for a more vanilla image, but eventually she did some things that rivaled the Ibuki Haruhi days. She turns out to be one of those people who can eat insane amounts of food (some people's stomachs can just stretch like that so they can eat forever), so she made a video fetishizing that. But people who do that also take enormous shits, so she made videos fetishizing that.
Check out the Dogma label. She has made easily some of the most extreme stuff for them, and that's saying a lot. There's one where she takes a shit that is literally 1 meter long. Also one where she is force-fucked until she vomits, then they give her an enema of her own vomit, and then for the finale they have her have sex in a pool filled with her own enema vomit.