I decided to mess around with the stats for a bit with some clever Notepad stuff, here's what I found. Apparently, it only counts which hole has the most amount of semen inside, sex count is mostly a vanity thing. I had sex count at 1 for each hole, and it even works at 0 sex count (how did she get semen inside her without sex count lol):
Stage 0: Don't get creampied on. You may get penetrated, but as long as your pleasure does not max out, you can easily masturbate to top it off. Also, apparently masturbating increases stamina faster, which is weird.
Stage 1: 0-249 mL inside (uterus or rectum, whichever is higher). Syahata is a little disgusted that someone creampied inside her.
Stage 2: 250-499 mL inside. Syahara looks to be stuck in climax due to the amount of cum inside. She probably laid some eggs at this point as well. Her crotch's messy as it drools some spunk from her honeypot. She would flash her panties when surrendering. Her lines would be slightly more accepting to whatever is going to rape her.
Stage 3: 500+ mL inside. Her mind virtually broken by being creampied, Syahara would be masturbating in her status screen, with some cum in her face and what looks to be breast milk dripping from her nipple (lactation is one of my fave fetishes). Her insides is pretty much filled up with cum at this point. Her surreder will have her stick her butt out for anyone to claim. Even her lines show that she became a bitch in heat!
I am not sure how the game will handle a 'virgin clear'. Basically, masturbating will pretty much flush down all your pleasure gained, and penetration doesn't count. Something tells me this stat might also affect endings, considering how there's this thing about 'evil fever, stage 2 infected' and stuff. Here's hoping Syahara is one of those immune types!
I know it might be much more work, but for some reason, I would like it if this game has a naked mode or something.