Hitsugi no Chaika: Nerawareta Hitsugi/Yomigaeru Iseki

While escaping from the Gillette Corps, Tooru and Chaika hide inside a theater.

After a couple of mishaps, they end up taking part in a stage performance along with Akari and Fredrika.

Later, the Saboteurs, the Gillette Corps and the Red Chaika's group go to the ancient ruins rumoured to contain Emperor Gaz's remains.

A three-way battle ensues as each party tries to obtain the remains first.

— written by Singan

Note: the OVA contains two side-stories for the first season.

The first one takes place somewhere between episode 4 and 6, and the second one takes place somewhere between episode 6 and 10.

The OVA was bundled with the 12th Hitsugi no Chaika novel volume.