Disclaimer: I don't own Fire Emblem Three Houses, all rights to the owners.
I got a few more ideas, so I'm throwing them at you. Here ya go.
"Would you listen already?"
"..."
"Hey! I'm talking here! Listen to me!"
"Go away."
"I can't! I'm in your head."
"You're a ghost. Go away."
"A ghost!? How rude! I may be in your head, but I am no ghost! At worst I am a spirit conjoined to yourself!"
"That sounds like a ghost."
"And you sound like a child! Do you hear yourself? A ghost, really. You offend me."
"If I offend you enough, will you leave?"
"I can't. I've said this already."
"Maybe I've been poisoned, and you're a hallucination. It would have to be someone in the mercenary company who's responsible, since I've been hearing you before I got to the monastery." Byleth mutters to himself. "Acrim maybe? Or Laurence…"
Sothis sighs in defeat. This isn't the first time she's failed to convince Byleth of what she is, and it probably won't be the last.
###
"You work too much."
"Says the pot to the kettle." Edelgard responds evenly. "I am to be emperor eventually Professor. It would reflect badly on the Hresvelg line for me to not overwork myself. Besides, there is far too much to do, and too little time. A lack of sleep is a small price to pay. You do the same yourself, do you not?"
"Maybe." Byelth blinks. "But that doesn't mean I'm wrong. You work to much. You need to relax."
"With all due respect Professor, I don't have time for that."
"You have free time this afternoon."
"I do not. I have paperwork-"
"Ferdinand has paperwork, and will report to you tomorrow morning." Byleth cuts in. He raises his voice a bit. "Right Hubert?"
"Indeed." The boy says, and steps into the doorframe from where he was hiding just outside.
"Don't tell me you're in on this plot too Hubert…" Edelgard sighs.
"Of course I am Lady Edelgard. Your health is paramount, and you are overworking yourself." Hubert says in a tone that almost sounds smug. "Do not worry, I've sorted more sensitive documents out of the pile."
"Surely Ferdinand did not agree to-"
"He did." Byleth interrupts.
"He practically jumped at the chance to help… after I suggested it might be a way to upstage you, your Highness." Hubert smirks. "Such an easy man to manipulate…"
Edelgard sighs deeply. These two… "I thank you for your concern, but I am not going to waste my time-"
"It's not optional." Byelth interrupts again. He glances at the window. "In fact, it's time to go. Come."
Without waiting for her to even finish her current work, he grabs her around the waist and throws her over his shoulder like he has so many others… usually ones named Bernadetta, but other people too. Usually women for whatever reason.
Edelgard shoots Hubert a pleading look, but the boy just bows and says "enjoy your night off, your Highness."
The girl processes her situation as Byleth carries her down the stairs, and eventually resigns herself to the fact that she's not going to be allowed to work tonight. "So, I presume you have a plan Professor? Or were you just planning to carry me around the monastery until something occurred to you?"
"I… do."
"You don't sound certain."
"I was informed earlier by Marshmallow that my idea of relaxation is apparently not appropriate for students."
Edelgard is afraid to ask, but she does. "And what was that idea, pray tell?"
"Beer, cards, and sex."
If the princess had a drink, she would have spit it out. "Pardon!?" That was not what she expected from the professor.
"That's how the mercenaries of Father's company always relaxed. Apparently that's not appropriate for students."
"I dare say it's not…" Edelgard says in disbelief. "How did that conversation even come about?"
"Marshmallow asked me what I do to relax, I said I don't. She asked me if I knew how to relax, and I said yes, and that to relax you go to a pub, get drunk, play cards, and have sex." Byelth says with a totally straight face. "She informed me that those things are not the only way to relax. I was not aware of that."
Edelgard can hardly believe he had that conversation with a student. Thank the stars it was Mercedes, who is extremely level-headed and tolerant of the professor's weirdness. If the professor had that conversation with someone like Flayn… or really just anyone that's not Mercedes, Edelgard, Hubert, or Claude, it might have reflected very poorly on him.
"Have you ever relaxed before?" Edelgard asks slowly.
"No. I never had the time. I just knew that's how you were supposed to relax, because that's how everyone else relaxed." Byleth says flatly. "At least, that's what they told me they did. I never went, so I didn't know."
Something occurs to Edelgard. "Professor… you weren't, by chance, planning to take me to a pub tonight before you had that conversation, were you?"
"Maybe."
"Has that plan changed?"
"...maybe not."
"Oh dear. The professor might need this as much as I do, if just for instructional purposes." Edelgard sighs. "Alright Professor, put me down. We'll find something else to do… together."
###
"Professor…" Seteth says through gritted teeth. "I thought I told you not let Flayn into the lake."
"She's not in the lake. She's above it." Byleth replies calmly. He's not looking away from the bait surrounding him in the water. "We're fishing."
"I can see that… usually one stands on the docks for such a thing Professor, or uses a boat."
"Usually." Byleth agrees. He doesn't comment further.
"Professor."
"Yes?"
"Why is Flayn stabbing fish with a stick while sitting on your shoulders, and why are you standing shirtless while waist-deep in the water?"
"Because I can see the fish better here, and I was warm." Byleth says as if it's the most obvious thing in the world. "And Flayn didn't want to fish from the dock."
"I was thinking of a boat myself, but this is a very enjoyable means of fishing as well." The girl says happily. "You should try this Brother! It is most fun!"
"I must decline…" The man says dryly. He watches as Flayn suddenly thrusts the stick forwards, but she just narrowly misses the fish that was was nibbling at the bait on the surface of the water. "Would not a fishing rod be more practical?"
"If you learn to fish with a sharpened stick, you'll never be at a loss for how to get food in a survival situation." Byleth replies bluntly.
"Need I remind you this is not a survival situation? Unless you have forgotten that the student's mess hall is not just for students again."
"I didn't. This is how I fish. Flayn wanted to learn. So I'm teaching, because I am a teacher."
Seteth sighs again. There's no arguing with this man. There's no way the professor can be a good influence on Flayn… which makes it all the more frustrating that Flayn is so fond of him. Still, there are worse people she could spend time with, like a boy…
His blood boils just thinking about such a thing.
###
"Why are the songs so boring?" Byelth asks.
Rhea's eye twitches. "They are hymns, meant to give praise to the goddess. They are not mere songs."
"That doesn't explain why they're boring. You could sin- hymn about the goddess in a more entertaining manner. Like rock, or swing, or maybe disco..."
"No." The Archbishop says instantly. "And hymn is not a verb professor. One does not hymn."
"But you sing a song, so wouldn't you hymn a hymn? Or maybe you'd hum a hymn… hmm…"
Rhea honestly wishes she could be anywhere else in the world right now, or, better yet, that the Professor was anywhere else in the world. Why does every meeting with him devolve into him asking annoying questions?
"Why do we hum to the goddess if she's in the sky? How can she hear us? Is she using magic? Doesn't she have better things to do than listen to people hum? How does she have free time to listen to people humming if she's supposed to be watching over the world?"
Why does only she get these questions? Why doesn't Seteth have to deal with this?
###
"O-Oh no! I'm not letting you get me again! Get back y-you demon!" Bernadetta yelps.
Byleth keeps walking towards her menacingly, with a hand extended to grab her. His neutral expression looks calculating to her, and Bernadetta feels like she's being cornered when she steps back and her heel hits the stone wall.
"Stay back! I'm w-warning you!"
The professor isn't listening. Bernadetta glances to each side, checking her escape routes. One side leads to the dining hall, which is bad. There's a lot of people in the dining hall, and if they see her rush in, they'll stare at her, judgingly, and then she'll always be known as the girl who barged into the main hall, and people will talk about her behind her back, and some of them will be mad because she surprised them, and they'll decide to remove that annoyance! By barging into the dining hall, she'll die!
So clearly she needs to go the other way. She slowly slides down the wall, and when Byleth is only an arm's length away, she bolts. She springs as quickly as she can, flying past the graveyard, the training pit, and the stables. She glances over her shoulder and shrieks upon seeing Byleth chasing her in a dead sprint.
The girl takes a sharp turn and dashes past the front entrance and the marketplace and moves into the pond area. She thinks the gatekeeper calls out a greeting, but she moves too fast to properly hear. Bernadetta nearly bowls over Ashe in her rush, and when she glances back again she sees Byleth just flat-out jump over the boy.
"Where do I go, where do I go?" Bernadetta asks herself in a panic. "My room? My room!"
She pulls out her keys and skids to a stop in front of her door. The girl frantically jams her keys into the lock, twists it, opens the door, and slams it behind her. She twists the lock as soon as she's inside to stop Byleth from opening it up. She slumps against the door and breathes a shaky sigh of relief.
Then the window slides open.
Byleth slips into the room like some sort of demon through a hell portal. Bernadetta scrambles to open her lock and her door, but Byleth grabs her arm, stopping her. The girl quails when he reaches out his other hand towards her and…
...fixes a button that had come undone. Then he leaves.
Bernadetta stares at his retreating form, then the button, decides now would be a good time for a nap, and collapses on her bed, emotionally and physically exhausted.
###
Caspar yelps as Felix is sent flying into him, and the two boys sprawl out on the floor for a moment before scrambling back to their feet. They try to rush back at their foe, but he trips their other ally, Leonie, causing them all to stumble over themselves.
"You're not working together." The professor says flatly. "You're literally tripping over each other."
"We're from different classes Professor!" Caspar protests. He moves to the left, trying to cut off the man's escape and box him into a corner. Byleth instead slips through the middle, because both Leonie and Felix both went left, leaving a hole in their line. "We're not used to fighting together."
"That is true, but soldiers of different groups should be able to at least use basic tactics alongside each other, even if there was a language barrier." Byleth responds flatly. His sword licks out to swat Leonie's lance aside when the girl steps towards him, and it intimidates her into not trying again.
Felix and Caspar go on the offensive, rushing the professor's flanks. Rather than outdo them with his tactics like he was before, the professor outskills them with good swordplay, managing to keep his weapon moving quickly enough to block both of their attacks. Even when Leonie joins, they're having trouble landing a hit.
Suddenly Byleth ducks low and sweeps his leg, catching Caspar and tripping him. While still in a squat he pushes off the ground and launches himself at Leonie, who didn't manage to get her spear in the way in time. He tackles her, bringing them both to the ground, but he them tightly wraps an arm around her neck and hauls her to her feet, and uses her as a shield to stop Felix from attacking him.
"A human shield?" Felix growls. "Have you no shame?"
"There's no place for shame in a battle." Byleth responds evenly. "Use every advantage you can get. Bring a meteor to a fist fight if you can spare the resources. Only a fool, or a dead man, thinks of chivalry in combat."
The fight goes downhill from there. Leonie gets eliminated when Byleth throws her on Felix's sword, Caspar falls next to a well-placed thrust, and Felix eventually gets defeated when Byleth manages to grab his arm, shoulder him in the face, and then slash his stomach.
"You three are individually good fighters, but your coordination could use work." Byleth remarks calmly. "Alright, next."
Edelgard, Dimitri, and Ferdinand all glance at each other. This isn't looking good for them already.
Just some miscellaneous ideas. I find the Black Eagles the easiest to work with. Maybe it's because Bernadetta, Edelgard, and Petra are characters I'm quite fond of, and Dorothea is quite easy to write as well. Really, the Black Eagle girls are just great; and Hubert. Hubert is good too. In other houses I have one or two characters I'm fond of (Dedue, Mercedes, Annette, Marianne, Ignatz), but in the Black Eagles I have five.
Also, I seem to have made a little saga about Byleth fucking around in the lake. I don't know what it is about that lake, but it's a goldmine for this story apparently.