There are a doujin version of this series before the start of the magazine version, which is basically the story of ch.1:
https://www.pixiv.net/artworks/68365324
Some of the difference of the doujin version from the recent series:
1.There are only two characters: Aya and Kurosaki.
2.They know each other from matching website.
3.Kurosaki is a smoker.
4.After tell Aya to come to her place, Kurosaki hang around in the bar and go home really late(but Aya wait for her anyway).
5.When Aya expressed her discomfort, Kurosaki continue and do everything.