Shimeji SimulationArt2013 Altogether

This picture was uploaded to Danbooru on May 19, 2013, so we can assume it was drawn in the same year. The drawing itself is actually pretty interesting:

  • Characters, to the right:

    • Umbrella #1 — Yocchan, Mina

    • Umbrella #2 — an unknown girl

    • Umbrella #3 — an unknown girl

    • Umbrella #4 — Shimeji-chan

    • Umbrella #5 — Yuuri and Chito

    • Umbrella #6 — three unknown girls. One of them is holding a closed umbrella.

This picture has both Mina and Shimeji, so theories about them being the same characters are proven to be false. That's quite interesting, because the Shimeji Simulation one-shot featured Mina, but the actual Shimeji Simulation manga features Shimeji. At which point tkmiz has decided Shimeji is better for the story?

The way Shimeji looks at the viewer reminds of some scene in the manga. Which one?