I had to re-read those first few pages over a few times before I could even move on with the story, that was sorta confusing. Mikumo slept with a senpai back in the day who she loved, only to get shelved. So when Kanon, her kouhai at the time, confessed to her, she pre-emptively rejected her first. Now they get a second chance, woo!
Sorry, I'm sure those longer posts explained this better in more detail, I just had to write it out to log it in my brain. I liked this, wish it had been a whole volume with more details.