How to get a lasting ahegao face (at least until version 1.4, the one I stopped updating after concluding Oni lost his thumbs when I saw Betsy and the eldritch abomination).
Each time you make the girl come
during the same intercourse, her Lust resets to 0 + (5 x number of previous orgasms).
After you made her orgasm 5 times (Lust just resets to 25), she'll say she has had enough and ask you to stop what you're doing (she has her ahegao face when asking, but it won't last for now). You can either agree and switch to another sex act or if your focus was on, agree to release it and keep going (nothing prevents you from reactivating your focus immediately after). Or you can stop here and forget this ahegao business, but I don't think you will.
Keep giving her orgasms and she'll ends up making her ahegao face again and this time, it'll stay on for the rest of the intercourse (I play prime mod 1.4 and it happens when her Lust resets to 50 but I seem to remember it happening at other milestones - 40 I believe - in other versions).
Sadly, once you exit the sex menu, the ahegao face disappears and has no lasting effects (there doesn't seem to be dialogs or events following you fucking the girl silly), but that's Oni for you: better add hideous characters than fleshing the existing ones and really make the game better, right?
