A special episode listed as 5.5 on bilibili.

When disaster strikes, how can we sincerely awaken the phoenix?

The anime takes place in 2006, and centers on Akio Hoshigami, who due to a leg injury is forced to give up on her dream of being a track-and-field star. Akio and her friend Ayano Umisoe move on to high school together. Amidst new activities and meeting new friends, Akio gradually starts acting like herself again. Then one day Ayano suddenly disappears.