The 23rd volume of Attack on Titan announced Attack on Titan: Lost Girls(Novel) will receive a 3 episode OVA adaptation. The OVA is set to release alongside the main manga. Episodes will be bundled with 24th volume, 25th volume, 26th volume of the Attack on Titan manga.
The novel collects three short stories centered around Mikasa and Annie titled, "Lost in the cruel world," "Wall Sina, Goodbye," and "Lost Girls"
The 24th volume, 25th volume will cover Annie 2 part Story. Part 1 will be released December 8, 2016 and Part 2 will release April 9, 2018. 26th volume will come with Part 3 that will Cover Mikasa Story it will release August 9, 2018.