[Once the door is shut, Felix carefully takes out the dagger entrusted to him, unwrapping it from the cloth as he places it on the table.]

It's... the Flame Emperor's. Dimitri... asked if you could return it to her.

[It should, perhaps, tell Byleth everything he needs to know about how the dagger came to his possession in the first place.]

I've... also decided, [Felix says, exhaling as he trains his gaze on the dagger.] I know the side I truly belong to. No matter what happens, I'll do everything I can to make sure Dimitri lives.