As a typhoon approached to the town, the girls remembered a time when they went ghost hunting four years ago (during a typhoon too). The girls had trouble remembering what happened and asked the rock to help them remember. The rock transported the younger versions of the girls to the present. It was a very entertaining episode with a cool revelation (I do not want to spoil it and would take a while to explain). At the end of episode 10, Yuka revealed that she signed up the girls for an audition for an idol group.
This was a very good, fun and entertaining episode. Despite being back to the town setting, the content felt fresher. I had a good laugh watching the mischievous young versions of the girls squabble with their older counterparts. I think this is the best episode of the series so far. Episode 10 of Natsuiro Kiseki also proves that the creators of the series can make episodes that do not feel redundant and boring. This episode gets a solid and strong 9 out of 10.