Attack on Titan (OVA)

It is an OVA miniseries belonging to the anime series Attack on Titan.

Ilse's Notebook
Ilse's Notebook is the first trilogy of OVAs from the Attack on Titan anime, produced by Wit Studio and Production I.G, and included with a limited edition of Volume 12.

No Regrets
No Regrets is the anime adaptation of the Attack on Titan: No Regrets manga that narrates Levi's past, included in volumes 15 and 16.