Kanon spin-off OVA bundled with vol. 22 of the Kami nomi zo Shiru Sekai manga.

An exoskeleton weapon engineered by Japan, Infinite Stratos (IS) can be piloted only by women. Its power and combat prowess are so immense that an international treaty has been signed banning its use as a military asset. When it is discovered that 15-year-old Ichika Orimura is the only male capable of steering an IS, he is forcibly enrolled in the Infinite Stratos Academy: an all-female boarding school, the students of which graduate to become IS pilots. At this training school, Ichika is reunited with two of his childhood friends, Houki Shinonono and Lingyin Huang, and befriends Cecilia Alcott, an IS representative from the United Kingdom. Guided by the legendary pilot Chifuyu Orimura—their strict homeroom teacher and Ichika's older sister—Ichika and the girls will need to use everything at their disposal to defend themselves and their academy against the dangers that will arise during the course of their thrilling school life. [Written by MAL Rewrite]

Life gets crazy for Hakufu when she takes on a pupil that acts just like her! A tournament between the school heads start, but due to Hakufu's negligence, her pupil ends up taking her place. The tournament isn't what it seems, and the girls find themselves in the middle of a plot to take over the clans. (Source: FUNimation)

Hakufu's dreams of participating in new fights and tournaments are put on hold as new obstacles block her path. Her friends have lost faith in her, new enemies appear, and a younger sister she never knew existed suddenly shows up on her doorstep. If Hakufu ever hopes to compete worldwide, she's going to have to deal with her issues at home first. (Source: FUNimation)