
When step siblings go grow up as siblings you're siblings.
But here they've never even treated each other as siblings. She was a dick to him until new her showed up and then he was sent to the Academy. And since it wasn't mentioned the funeral is probably the first time they had seen one another since he left. They're basically 2 Acquaintances living in the same house
As much as i want a yuri in a historical setting ,incest is a no