In the game Yumiko has a drink with you, and if you get an erection, she give you a bj. If you don't get an erection, she sends you pics of her meeting with Joy. If you don't get an erection a second time, she offers to start playing the game with you.
A couple of suggestions for 5.1:
In my opinion this should be reversed for two reasons. One, it takes a long time to finish the game, so starting it earlier would mean it ends earlier which is better timing for when the majority of content runs out. Two, Yumiko's bikini pics come at the same time as the other girls start sending sexts which make Yumiko's less special. (Also, Yumiko should send one a day instead of three in one day and then not send them again.)
Perhaps the game could have its own quest to start. For instance, when Yumiko sends you her first pic, have a line that she'll be taking pics of he girls to send you to see if you can recognize them, but first you have to buy me some expensive perfume and give it to me when I'm working.
Just a minor idea.