So for starters here is what you need for the CG at the top left of the second page. To get it you need to buy the doctors outfit and Shuu will say that they should do a doctor role-play but since they aren't in a doctors office then he doesn't think it fits right. A few days later he should approach you after classes and take you to this shady doctors office place from which you'll get the CG.
Next up is the CG on the mid right which should be pretty simple. From what I know you just have to use your mouth on his dick three times in a row and you'll suck his dick. I'm not sure but I'm pretty sure it's random chance that sometimes they will say I want to pleasure you too so you get him in the 69 position CG. That same thing applies for the first chibi on the top left since it's just the 69 position one.
The next chibi you should get either when you are at max love and kiss him or at random. Still don't know which one.
The one near the bottom and to the left should just be the one which you use your mouth on his ass three times and as for the last one you'll need to make Shuu change his preference to bottom sub and he'll eventually suck your fingers as a result.
Hope I'm not too late my dude and have fun! <3