And here's Machi with her casual wear. We saw Machi wearing this specific outfit during her "date" with Takahashi-Sensei during the series, the blue in her shirt bringing out her bright blue eyes. Notice in the background scenery it shows what appears to be a cafe umbrella, as well as some shops. We can safely assume that it's some sort of entertainment or shopping district. This may be a direct connection to her date with Sensei, as that seems to be the moment when they fully build a bond. Things had been working up to that, but it was on the experiment date that they built a deeper teacher-student relationship, and Takahashi further understood the depth of a dulalhan's nature.
We also see Yuki, the cutest little snow woman. Throughout a good portion of the series, we see her struggling with her snow woman nature. Over time, she finally comes to accept herself, and realize she doesn't need to be afraid anymore. One of the more defining moments of her change was her opening up to Machi and Hikari. After putting so much distance between her and them, Yuki decided to take the step and reach out to them, building strong relationships. It was right after they had gotten ice cream together, and she sincerely told them about her feelings. It was then that she realized she didn't need to be so reserved from her peers, and she was able to break free of all of her restraints. In the background of the artwork, we see what looks like the scenery from this ice cream encounter.
The theme of these art pieces seems to be the significant changes for the Demi-chans. In the backgrounds is all scenes where they seemed to bloom into themselves, to fully embrace their Demi-chan nature and starts growing as people. The music event is sure to be an incredible hit, and hopefully, it will show up in the US at some point. Cheers to our sweet Demi-chans, we miss them!