The Valkyria Chronicles series tends to have hidden characters that require you to allow someone to fall in battle to make someone new appear. Valkyria Chronicles 4 is no different. The good news is, you can get one of these special characters really soon! All you have to do is sacrifice Curtis Blackwell to make Eileen Blackwell appear.
Curtis Blackwell is a scout you have access to immediately in Valkyria Chronicles 4. He is a rather average character. What you want to do is deploy him on a map, then run him right up to an enemy. A shocktrooper or engineer would be preferred, though an opposing scout or lancer would work. You then let him fall in battle. Just make sure you also send another character over to reclaim his body so Karen the medic can rescue him after.
After Curtis falls in battle, you will have a new recruit join Squad E. It is Eileen Blackwell, Curtis’ engineer sister. Once she joins, his preferences and potentials will change. He will then like both Laurent and Eileen. He will also have the Overbearing Sister potential, which makes his accuracy drop if she is around.
Meanwhile, Eileen likes Curtis, Laurent, and Brittany. She has two potentials that relate to her brother. Distracted kicks in when she is not around Curtis, lowering her defense, and Unreliable Brother kicks in when both she and Curtis are deployed at once, decreasing her evasion when he is around.
Valkyria Chronicles 4 is available for the Nintendo Switch, PlayStation 4, Xbox One, and PC.