Long but worth it. This comes from an omake/parody of a fanfiction I read some time ago.
The moment he entered the room, Byleth's eyes landed on the large knight in the center of the mausoleum.
"That must be the rumored Death Knight," he muttered to himself. "He certainly fits the name."
Towering over everyone else on his black-armored horse (how did that horse even get in here?), the Death Knight's red eyes shined brightly from within his skull-shaped helmet. His dark armor was adorned with a ridiculous amount of spikes that seemed more nonsensical than practical, and he lazily held a black scythe in his hands. Wisps of inky smoke seemed to come from the blade, giving it an eerie look.
But that wasn't the reason why Byleth was looking at the Death Knight. He didn't care about the spiky armor or the smoky scythe. No, what he was focusing on was a tiny trinket hanging off his belt.
"That's…the Death Knight!" Edelgard hissed. "Teacher. He is a powerful enemy. We should do our best to avoid him."
She said it as if she knew it for a fact, not something based off of rumors. Almost as if she knew of the Death Knight prior to today.
Byleth nodded and began to walk towards the center of the mausoleum.
"T-Teacher?" "Professor!"
His student's voices, heavily laced with confusion and worry, reached his ears.
"I heard you loud and clear, Edelgard," Byleth said. "But I still want to beat him."
The Death Knight clearly heard Byleth, evident by how his eyes gleamed maliciously from the helmet's eye sockets.
"Why, Teacher?" Edelgard asked. "He is a dangerous foe! There is no need for us to fight him! He even said that he wouldn't fight us unless provoked first!"
Byleth didn't respond as he continued to walk forward. He unhooked his sword from his hip and held it out to the side while keeping his gaze focused on the Death Knight. In return, the Death Knight slid off his horse, and Byleth got a feeling that he was grinning from behind his helmet.
"Oh? You're approaching me?" the Death Knight rasped. His voiced sounded metallic and hollow, almost as if there was nothing beneath the armor. "Instead of running away, you're coming right to me? Even though your House Leader told you how dangerous it is, like a student scrambling to finish the problems on an exam until the last moments before the chime?"
"I can't get that Dark Seal from you without getting closer," Byleth cooly replied.
"Oh ho!" The Death Knight expertly twirled his scythe his hs arms. "Then come as close as you'd like."