Posting this here because it's my largest fan story endeavour yet, and it'd be a shame not to share it to a wider audiences due to the effort put into it. You may also find it on AO3 and SpaceBattles.
Archive of Our Own
SpaceBattles
QuestionableQuesting
Ymir is a born again, haunted by the memories of the boy she killed and the past life she once lived. In order to put her mind to rest she must uncover the truth behind her past, even if it means reliving it once, twice, three times more. Along the way she meets a girl who craves to be special; something that her father couldn't be and so much more. This girl's name is Historia, and though the two of them are often at odds their fates are intertwined, both inheritors of a legacy that was too much for one goddess alone to bear.
The Year is 845.
This is the year that a girl reawakens, another fights back, and a third, a harsh mistress, is born.
This is the story of those who are caged no more.
Part 1 Point of View Characters
Other Characters Mathias Kramer - scion of the Kramer Merchant Association
Rita Iglehaut - member of the Garrison, West Division (Quinta)
Ada (original character) - survivor outside the Walls
Kelly - leader of the survivors outside the Walls
Amanda - member of the Garrison, West Division (Quinta); Rita's best friend
Klaus - member of the outlaws
Nikki - member of the outlaws
Jörg Kramer - Mathias's father; head of the Kramer Merchant Association
Isolde Lenz (original character) - farmer; Riecka's mother
"Baggy-pants" Leon - member of the Garrison, West Division (Fuerth)
Kenny Ackerman - member of the Military Police Brigade
Doris Iglehaut - Rita's adoptive mother
Henning Iglehaut - Rita's adoptive father
Ducio - member of the Garrison Regiment, West Division (Quinta); Rita's assistant
Wilco - member of the Garrison Regiment, West Division (Quinta)
Bernhardt - leader of the outlaws
Jarratt - member of the outlaws
Gabriel - agent of the Royal Government
Erhardt - member of the Military Police Brigade
Sources
Attack on Titan written and illustrated by Isayama Hajime.
Attack on Titan: No Regrets written by Gun Snark and illustrated by Suruga Hikaru.
Attack on Titan: Before the Fall written by Suzukaze Ryō and illustrated by Shibamoto Thores.
Attack on Titan: Harsh Mistress of the City written by Kawakami Ryō and illustrated by Murata Range.
Attack on Titan: Lost Girls written by Seko Hiroshi and illustrated by Fuji Ryosuke.
Attack on Titan: Wings of Freedom (video game) based on the manga written and illustrated by Isayama Hajime.
Attack on Titan Guidebook: INSIDE & OUTSIDE based on the manga written and illustrated by Isayama Hajime.
Attack on Titan Choose Your Path Adventure: Last Stand At Wall Rose written by Fujinami Tomoyuki and illustrated by Fuji Ryosuke and Yoshii Tetsu based on the manga written and illustrated by Isayama Hajime.
Attack on Titan: End of the World written by Asakura Touji based on the manga written and illustrated by Isayama Hajime.
Garrison Girl: An Attack on Titan Novel written by Rachel Aaron based on the manga written and illustrated by Isayama Hajime.
Sources (Doujinshi)
A Distant Fragrance written and illustrated by Tokawa.
MESSENGER written and illustrated by Tomo.
Story of the Goddess Who Sought Death written and illustrated by Kuzumochi Shio.
Night at the Hut in the Mountain (and other shorts) written and illustrated by tbtbii.
Song of Prayer Dedicated to You written and illustrated by Poncho.