Seryuu's a member of the Jaegers, having transferred from the Imperial Guard. Her whole worldview basically revolves around "Justice"—something that got hammered into her after her father died serving in the Imperial Army. She also idolized her mentor Ogre the Demon and took his death hard.
Here's the thing though: her idea of justice is pretty warped. She sees Night Raid as irredeemable villains for being assassins, but she's totally fine with killing in the name of justice. Which, funny enough, makes her moral code almost identical to theirs—just wrapped in different packaging. She operates on a strict black-and-white view of the world. If you serve the empire, you're good, period. If you oppose it, you're evil, no exceptions, even if you were forced into it. She genuinely can't see the gray area.
This twisted perspective has made even her own teammates wary of her. There was an incident where she murdered a group of prisoners before anyone could actually interrogate them—a move that earned her some serious side-eye from the broader imperial forces too. For someone obsessed with justice, she's basically become a liability to everyone around her.
Content compiled by AnimeList.moe from publicly available sources.