The 23rd volume of Attack on Titan announced Attack on Titan: Lost Girls (Novel) will receive a 3 episode OVA adaptation. The OVA will release alongside the main manga. Episodes will be coming out along with the 24th volume, 25th volume, 26th volume of the Attack on Titan manga. With this Attack on Titan Novel receaving an anime adaptation, fans of AoT have a good reason to cheer.
Attack on Titan Novel Summary
The novel collects three short stories centered around Mikasa and Annie titled, “Lost in the cruel world,” “Wall Sina, Goodbye,” and “Lost Girls”
Attack on Titan: Lost Girls is a novel and compilation of three stories written by Hiroshi Seko, a scriptwriter for the Attack on Titan anime. The first two stories, “Lost in the Cruel World” and “Wall Sina, Goodbye” are based on the visual novels of the same names, released on the Blu-ray copies of the anime. A third story, “Lost Girls,” was a new release. The three stories were also adapted into a manga of the same name. (Source: Wiki)
Furthermore, check this Attack on Titan Season 3 Releases Promo Video, To Premiere on July 22, 2018
LOST GIRLS tells of the times and spaces in between the plot points, through the eyes and ears of the saga‘s toughest – but more taciturn – heroines. What they thought, and felt, and did on and off stage come to the fore via a medium distinctly suited to conveying interiority: language.
The two novella-length offerings were originally included as bonus features in the initial Japanese Blu-ray released, while the introduction and the titular story are unique to the book. A manga rendering of this official spinoff is slated to appear stateside from Kodansha Comics. (Source: Wiki)
The 24th volume, 25th volume will cover Annie 2 part Story. Part 1 will release on December 8, 2016 while the Part 2 will release on April 9, 2018. 26th volume will come with Part 3 that will Cover Mikasa Story it will release August 9, 2018.