I wish there was like a more concrete way we can get pinged for people when they respond to these things lol. To get the doggo CG, Shiba has to be completely submissive, he can't be on top when y'all boink, ever. Then there will come a scene during the week where y'all meet in the park, he sees the cute doggy, picks it up, it licks his cheek, etc.
After Shiba leaves, you will encounter the Love Hotel suit wearing person and a prompt will pop up. I forget what it is. Anyway! I think it's a sex toy that it will be trying to give you, get it and the next time y'all meet up, it'll automatically do the scene.
I'll be going through this again for y'all since I messed up with my version on my laptop :/