Disclaimer: I don't own Fire Emblem Three Houses, all rights to the owners.

A few new ideas and a minor broadening of scope. Also yes, I know you don't just have a towel in the sauna, and that it's not gender locked. I'm using artistic license here, sue me!

Wakefulness comes slowly to Bernadetta. For once she feels rested and calm, and ready to face the day.

Then she actually opens her eyes.

Byleth's own dull green eyes bore into hers. They look huge, in no small part because his face is currently hovering less than an inch above hers. Bernadetta freezes in place. If Byleth were to breath out, she'd be able to feel it, though he isn't… somehow. Does he not breath?

"Bernadetta." He says calmly. "Class is in five minutes."

The girl is too paralyzed to actually say anything. Her hands grip her sheets and she shrinks into them, trying to pull them up to protect herself.

"You must get up." Byleth says. "Move. Now. You will be late."

When Bernadetta doesn't immediately move, Byleth moves so close that their noses bump. The girl feels like she's going to pass out.

"Move."

"D-Don't kill me!" She yelps.

"Move."

"Move or he'll kill me!? Oh gods!" Bernadetta scrambles out of her bed and starts grabbing her things. Everywhere she moves Byleth stays inches behind her, staring at the back of her head the entire time. She grabs her notes and her quill case and runs out the door.

She can hear the professor's footsteps behind her, and Bernadetta fears that if she looks back she'll see the man running after her, still staring.

The girl runs into the classroom, panting, to the surprise of her classmates. Bernadetta can feel their judging eyes on her as she sits in the back of the class and hides behind a pillar.

Byleth, apparently satisfied, moves to the front of the classroom to start teaching. Through his expression doesn't change, Bernadetta can swear he looks smug.

"Professor!" Ferdinand shouts, holding up a hand. "I must protest to you chasing Bernadetta around in her nightwear! Even if it is to get her to class!"

Bernadetta blinks, and glances at her outfit. Her cheeks burn red and her limbs start to tremble as she realizes that she is indeed still her in her nightclothes. She was in such a panic to get to class with the professor staring at her that she forgot to change.

"She is in class, that is what matters." Byleth responds flatly. "Appearances are not relevant."

"I beg to differ!" Ferdinand protests.

"Noted and ignored." The professor replies. "Now-"

"Professor." Edelgard says sharply. "I agree with Ferdinand, for once. You may not care about modesty, but the rest of us, and Bernadetta, do."

"Fine." He turns around, tears off a curtain, marches over to Bernadetta, and wraps it around her. "There. We can work now."

"Do you know how many times we've had to replace those in the last few months?" Ferdinand groans.

"Several." Byleth says without remorse. "They are useful tools."

"They are decorations Professor."

"Everything is a tool waiting to be used. Usually to smash someone's head in, but in this case for modesty."

Edelgard shakes her head as Ferdinand continues to argue. She knows he won't win this fight.

###

"Marshmallow."

"Professor!" Mercedes blinks. "Erm, hello."

"I did as you suggested." Byleth reports. "I did not carry her, nor did I get someone else to carry her."

"Bernadetta I presume? Good."

"I employed social skills instead." Byleth says. Mercedes can hear a bit of pride in his voice.

"Wonderful." She smiles, and then glances around. "Erm…"

"I used intimidation. I stared at her, intensely, until she did what I wanted."

"Oh dear…" The older girl sighs. "We must talk about that later Professor."

He tilts his head. "Why not now?"

"In case you haven't noticed, I'm in the sauna."

"As am I."

"It's the ladies' time Professor."

He visibly frowns, just a little bit. "There are certain times?"

"Yes, did you not see the schedule?"

"There's a schedule?" He blinks again. "It's separated by gender?"

Mercedes sighs deeply, albeit fondly. She can't even say she finds this unusual anymore. "Yes Professor. It's attached to the board out front."

"I see... or, I will see. When I check. In a moment."

"Good." The girl nods. "Now, erm... You should leave Professor, preferably without being seen."

"Is being seen bad?"

"In this case, yes."

"Okay." He moves towards the window, pulling something out of his pocket.

"Do not break the window."

He frowns again. "How do I get out then?"

"Use the front entrance, like everyone else."

"But then I might get seen. You said not to be seen."

"I said preferably without being seen. To be honest, I don't think most of the students will do more than raise an eyebrow. I'm only really worried about Seteth." Mercedes explains. "Just leave Professor."

"You sound tense."

"I happen to have a man standing before me while I'm dressed only in a towel."

"Oh… is that bad?"

"Less bad and more extremely uncomfortable."

"I see." He blinks. "Who is the intruder?"

"You Professor."

"Oh." He blinks again. "I see." He turns around. "I will leave."

"Good. I will see you later Professor."

"The same time as usual?"

"Yes Professor."

"Should I bring food or are you-?"

"I'll bring the snacks as usual Professor."

"Okay. Should-"

"Professor." Mercedes interrupts. "Leave please."

"Okay…"

Byleth marches out of the sauna. He nods to Annette, who was just entering, and ignores her startled "Eep!" as she makes sure her towel is covering her.

Annette steps tentatively inside the sauna, glancing over her shoulder to make sure Byleth didn't follow her back. She hears a long, drawn-out sigh from inside and notices Mercedes.

"Mercie, was he…?"

"Yes, don't worry about it." The older girl says. "It's fine."

Annette shakes her head. "I don't see how you put up with him."

Mercedes smiles. "Oh, he's not so bad. Strange, perhaps, but nice; or at least well-intentioned."

"If you say so…" The smaller girl says doubtfully.

###

"The Professor's been holding back on us." Sylvain mutters, clenching the shaft of his spear. He drives it roughly into the archer in front of him, killing him.

"Shut up and fight." Felix growls.

"It's true though!"

"I know, but we have bigger concerns."

You would almost think the battle was staged from how it looked. The bulk of the fighting took place in a circle around the central pathway, between the Blue Lions and an unknown force among coffins of unknown contents. The center of the room is avoided by everyone except the two people already fighting there.

The Death Knight cut an imposing figure, standing tall with the help of his horse. That lasted all of one minute before he was knocked off, and is now fighting on foot in his dramatically spiked armor against Byleth, who is showing a level of competence much higher than he ever showed while sparring.

"Always keep an ace in your sleeve, that's what you told us." Dimitri mutters as he cuts down a mage and glances at his teacher. "You held back on us teacher, so no one would know what you can really do. Clever."

The incident of him beating Catherine into submission crosses his mind. That was holding back. A demon indeed…

It's not that Byleth is particularly fast or strong, but he's flexible to an unprecedented degree, and apparently quite the improvisational acrobat. His pinpoint accuracy with dagger throws, forcing the Death Knight to constantly twist his head to avoid a dagger sliding through the eye slits on his helmet, are quite impressive too.

So while the Death Knight is using brute strength and speed to make massive, swift swings of his scythe, Byleth is leaping over or ducking under the attacks entirely, throwing daggers or swinging his sword in spare moments, and occasionally pulling out stupidly impractical, extremely flashy, nearly impossible moves, and doing them flawlessly, leaving no doubt he must have practiced these an incredible number of times to make them even possible, much less usable in a combat scenario.

For one such move he shouts to Felix for spare sword, which the boy obliges by tossing it in the man's direction. Byleth leaps up, kicks the Death Knight in the face to distract him, and uses that force to push off and gain distance so he can snatch the sword.

That's not the impractical part.

Holding the extra sword's hilt in a loose grip, he flicks it up in the air in front of him, spins himself in place, and sharply kicks the sword. His foot must have hit the hint, because instead of impaling him the blade goes spinning end-over-end at the Death Knight at high speed. The knight manages to move aside, but the spinning projectile still clips his shoulder and leaves a deep gouge in the metal pauldron.

"What the fuck Professor!?" Sylvain shouts from across the room. "Since when could you do that!?"

"Always!"

"What didn't you tell us, or show us!?"

"You never asked!" He barks. "Mage on your left! Ingrid, cover him! Mercedes, to Dedue!"

The battle eventually ends when the Blue Lions cut their way through all the other invaders, and the Death Knight, battered and dented and gouged from everything Byleth has thrown at him (literally, in many cases, up to and including the lid of a coffin or two), snarls and teleports away, warning of vengeance to come.

"Hey Professor!" Ashe calls. "One of the intruders pulled a weird sword out of a coffin!"

"Put it back. Not our problem." Byleth says curtly. "I'll report it to Rhea. She can deal with it."

"Professor!" Sylvain shouts, running up to the man. "You have to show me how to kick a sword."

"That's not hard. You take a sword, and kick it."

"No, I mean kick it through the air like you did."

"Oh. No."

"No!?"

"No." Byleth affirms. "Too hard, not worth it, unless you have a lot of extra time."

"Then why do you know how to do it?"

"I had a lot of extra time. Five years ago. Now I don't." He stares at Sylvain. "If you had enough time to learn to do that you wouldn't be doing your homework, which is unacceptable."

"Killjoy…"

###

"Feel better, now."

"Professor, that's not going to work." Claude says, clearly amused. "I mean, it might help, but that's not going to solve the problem."

Marianne gives her house leader a look that's clearly asking for help. The boy grins and gives her a thumbs up. That's not what she was hoping for. She wants Byleth to stop hugging her. Not get encouragement for it to continue.

The man stares down at her. "It's an order. I'm your teacher. Do it."

"It's not that simple…"

"Yes, it is." Byleth insists. "Do we need to have another party?"

"Oh goddess no."

Claude shrugs. "Hey, I wouldn't mind."

"No." Marianne repeats as firmly as she can. "Please, no."

"Are you sure?" Byleth asks.

"Yes."

"Do you need food? Food makes some people happy."

"I'm fine Professor."

"Do you need me to get a friend? Who are you friends with?"

"Really, I'm okay."

Byleth stares down at her and doesn't release his hug. "How about fishing. Do you like fishing? Do you want to fish?"

"Not particularly…"

His eyes narrow a bit. "There has to be something. I will find out."

"You're going to be dissapointed Professor…"

"I disagree. Happiness is mandatory, and you will follow the rules."

###

"Professor." Mercedes murmurs sympathetically. "I don't think Marianne's problem can be solved with a few hugs and some good food."

"What else does she need?"

"It's not a matter of just giving her things Professor. It's more of an emotional issue." The girl explains. "Which, unfortunately, is much harder to solve."

Byleth frowns. "Ah. Emotions."

"Professor, don't talk about them like you don't have any."

"I never said that. It's just that they tend to be more problematic than helpful."

"That's a very depressing way of looking at the world."

"It's true though."

Mercedes purses her lips. "I see them less as a problem or helpful and more as just who we are. To say your emotions are problematic would be like saying your hands are problematic."

"Depends on the situation then." Byleth says with total sincerity. "Sometimes hands get in the way. Usually the fingers. They can get caught on things."

That's not quite what Mercedes was going for, but she'd also be lying to say that emotions are never problematic, because sometimes they just aren't just your way of dealing with the world. Sometimes they are irrational, or not representative of what someone knows or thinks.

"I suppose that definition works." Mercedes agrees reluctantly. "Sometimes emotions are a problem. Sometimes."

"Sometimes." Byleth nods.

"And In Marianne's case, they aren't, because the problem is not the emotions but what's causing the emotions."

"If you say so."

"I do."

I think Mercedes is just a main character now. I'm also surprised how much mileage I've gotten out of the same gag with Bernadetta, and the curtains too.