Levi Ackerman. Humanities Strongest. Naturally stoic and has a firm wall built around his heart, even so it doesn't stop him from caring. He and Hange Zoe, alongside Erwin Smith and their friends Eren Jaeger, Armin Artlet, and Mikasa Ackerman volunteer to take Keith Shidis's place in training the cadets for the 110th devision. Which is where they meet Logan, Max, and Harriet. 

Lilith Riley. She grew up treated as royalty in the Underground. Her father was a soldier in the Survey Corps, which is where she got her passion for the military from. 

Her father died when she was only 16, and she no longer went by Lilith. She began going by Logan, as it had been her fathers name. When she turns 21 she enlists in the 110th training devision with her two sisters, Maxine Riley and Harriet Riley.

 But there's a catch; their all vampires. Afterwards, she serves as an assassin, taking out the most dangerous anomalies. Until she's tasked with joining an investigation with Levi and Hange, seeing as cadets and long time soldiers are all being targeted and killed in cold blood. 

Including her own sister.