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

Updates for this story are going to be much more infrequent. I consider it basically complete as is. Anything from here on out are just extras that cross my mind.

I'm taking an idea suggested by a reviewer (a guest by the name BlackAndGreenGriffon) in focusing on Petra for this chapter, mirroring the focus on Mercedes in Peculiar Professor. They don't have the same relationship dynamic at all, but just like Mercedes and that version of Byleth, Petra holds the potential to bring out more in this version of Byleth than other characters, because just like Mercedes and Peculiar Byleth, Petra is the only character where this Byleth acts as more than just their comedic premise.

"Professor. I have return."

"Returned." Byleth corrects, not looking up from her work. "Report."

"I did the spying on Hubert as you requested." Petra says. She carefully sits down on the wooden beam next to her teacher. They're up in the rafters of the Black Eagles classroom currently. It's just after lunch on a saturday. "It was… not perfect."

"Continue."

"I had done staying to shadows as we trained, and followed him from roofs. However, after an hour, he spoke to me. I do not know how long he knew I was there."

"As expected of Hubert." Byleth nods absently. "Did you learn anything?"

"Hubert walks very slowly."

The older woman snorts, amused. "Anything else?"

Petra shakes her head. Despite the professor not looking at her, she knows Byleth will know she nodded. "He did very little of note. It seemed as if he was taking a walk around this monastery. He went to out-of-the-way locations for a student, such as the storehouse and the knight's quarters."

"And that is not of note?"

"I do not think so. Am I wrong?"

"You tell me."

Petra frowns and thinks. "He is… planning to kill everyone through poisoning the food store and finding out where the best knights sleep so he can assassinate them."

"Maybe." Byleth nods again. "But there is another possibility."

"What Professor?"

"He was patrolling for threats. Hubert is constantly on alert for potential assassins and dangers to Edelgard. He was likely keeping an eye on the less guarded areas." Byleth explains. "The knights' quarters are not guarded as heavily because it is expected that the knights can handle themselves and resources are better spent on the students. The storehouse… it is guarded, but there is plenty of space to hide, and many things to tamper with that could be quite harmful. Food, spare weapons, crafting materials, all of them are essential to the running of the monastery."

"I see…"

"However, you could very well be right. It would do everyone well to be suspicious of Hubert." Byleth murmurs. "Your thoughts were valid, just remember that there is more than one possibility."

"Understood."

"Did you complete the secondary task?"

"Yes, I considered many ways to execute him… though I have concerns Professor."

"What?"

"I am concerning about being instructed to think about killing my classmates Professor."

"Concerned, not concerning." Byleth says. "Don't be worried about knowing how to kill people at any given moment. It's a necessary skill for an assassin. Besides, you never know when you'll have to kill a friend."

Petra blinks rapidly. Byleth keeps working as if nothing unusual happened, as if what she said was totally normal. Petra opens her mouth, closes it, then plucks up the courage to ask "Professor... have you had to kill a friend before?"

"Well, 'friend' might be a strong term, but I have had to kill members of my father's mercenaries before." She offers. "Sometimes they were long-term members too, who I'd known since I was young. They were very good at their facades, but I- well, usually Acrim at first- was a better investigator. We'd remove traitors and spies quietly, and Father would help grant the coverup for their death a level of legitimacy."

Petra hides a grimace. She has some worries about what the professor just said. "You claimed someone else, Acrim, found out first? How young were you when you had to remove someone?"

"Hmm… seven?" Byleth murmurs. "Or was it six…? It was just when I started my training."

Petra is appalled. "Your professor made you kill a teammate at six years of age?"

"Well no, she was in the process of removing someone when I found her, and I decided to help. It was no big deal."

Petra disagrees with that. That is very much a big deal. A child should not have to kill someone, especially a teammate, at such a young age. She stays quiet however. This does not seem like the time for an argument.

"Unless you have anything more to report, you're dismissed. Keep up your stealth practice. Remember to complete your tactics assignment for tomorrow as well." Byleth murmurs. She finally looks up with her usual fixed, fake smile on her face. "Good day Petra."

"Good day Professor." Petra murmurs, and quietly leaves the classroom.

###

"Professor, there are many skills needed to be an assassin, yes?"

"Of course." Byleth nods. "Like poisoning. I swung my hand over your drink earlier when pointing out Dedue, how do you know I didn't poison your drink?"

"Because you are my teacher, and would not do such a thing."

"Wrong answer, and untrue. If you were a problem, I would eliminate you by any means necessary, student or not." Byleth responds bluntly. "It is an assassin's job to never trust."

"I see." Petra says. "However, poisoning was not what I was referring to."

"What then?"

"You have often mentioned to class that seduction is a dangerous tool that assassins know how to use… however, you have not been teaching me any of the things about seduction."

"Correct."

Petra expected her teacher to elaborate, but Byleth doesn't say anything more. The Brigidine girl frowns slightly in confusion. "Why not?"

"I have reasons."

Petra may not be perfect with the language of Fodlan and all their social conventions, but she can recognize when someone is trying not to give a straight answer. It seems strange to her that her teacher would be reluctant to speak openly about this though. She usually has no issues talking about seduction and the use of sexuality, flirtation, and sex as it pertains to manipulation, spying, and assassination in class. To have her dance around the topic here seems odd and arbitrary.

"And what are those reasons?"

"Good reasons."

The purple-haired girl frowns. "What good reasons?"

"Ones that I have put much thought into."

Petra's frown grows deeper. Maybe she shouldn't push this. She takes a sip of her water, and immediately spits it out.

"I slipped some salt into your water. I even warned you I could have poisoned it." Byleth remarks flatly, and continues eating without missing a beat while Petra wipes water off herself. "Tsk."

###

"Professor, why do the monastery staff flee when you approach them?"

Byleth's eye twitches for a moment. She continues her training with renewed vigour. "I have a reputation."

"Yes…?"

"They think I am trying to kill them."

"I see." Petra blinks. "Why?"

"They think I tried to kill Sylvain when I dangled him off the walls, which isn't true, so now they all avoid me if I try to flirt with them."

"Flirt?"

"Yes." Byleth says curtly. Petra detects a bit of an edge in her tone. "When I am off duty."

"I see." Petra is slightly worried. People flee when the professor tries to talk with them? She can't help but feel bad for her teacher. From what Petra is aware, the professor barely has a social life to speak of, so the thought of her attempts to find new connections failing so miserably is saddening. "Do you wish for help in fixing-"

"No." Byleth says curtly, cutting her pupil off. "I can handle myself, thank you Petra."

"As you wish…"

###

It's four months into the school year when Petra realizes the professor doesn't trust her, or anyone for that matter.

Petra starts to realize this when she tries to put a hand on the professor's shoulder to get her attention, and the woman turns around (dodging her hand) before she can make contact.

Coincidence, surely. That's what she thinks at the time anyhow.

Then she sees the same thing happen when Edelgard tries to talk with her. So the next several times, Petra makes a conscious effort to try and lay a hand on the professor. Every single time the professor conveniently turns or moves at the last moment to prevent contact. The only time she allows contact is in sparring, and even then that only happens when she can abuse that contact (usually with a grapple or a cheap hit). Outside of sparring she never allows physical contact from anyone (with the sole exception of Jeralt).

It seems strange to Petra. She realizes Fodlan has a more reserved culture as a whole than Brigid, but the professor avoids even the most casual and harmless gestures, and the only other people she can think of who do similar things are Bernadetta (out of paranoia) and maybe Felix (because he's grouchy).

The conclusion that her avoidance comes from lack of trust is the obvious answer. Byleth is always warning her to be cautious of everyone, but Petra never considered that the professor might be cautious of her. It makes sense in retrospect, but it's a saddening realization.

Does she trust anyone aside from her father?

###

"Professor." Petra says firmly. "I am having concern about you."

"Really?" Byleth responds with a raised eyebrow. "How so?"

"I think you are paranoid professor."

"I am indeed." The lady agrees shamelessly. "Is that an issue?"

"I think yes." Petra frowns. "Professor, you do not seem to have any friends or close companions, you avoid any sort of touch out of what I presume is hyper-vigillence, you are constantly thinking about how to kill everyone around you, and I do not think you trust anyone… not even your own students, not me."

"Of course I don't." Byleth blinks. She says this as if it's obvious, as if there was never any question that she didn't trust them. The instant confirmation stings more than the realization itself did. Petra had felt a measure of closeness with her teacher, especially after being taken on as an apprentice, so this feels like a rejection to her. "I've taught you about this before, haven't I? Suspect everyone, be prepared to take out anyone, no exceptions. Never put yourself in a situation where you could be made vulnerable without a good reason and an escape plan, even if that situation is as simple as a handshake."

Petra doesn't consider herself emotional. Far from it. She's dealt with being what amounts to a political prisoner for years at this point, so she's had to have a good grasp on her emotions. Still, she can't stop her hands from trembling a bit. Anger? Sadness? Both? Something else? Something though, certainly something, and that seems to Petra to be more than Byleth can manage. "I trusted you Professor."

"A mistake." Byleth responds flatly. "It's safer, physically and emotionally, not to do that."

"As you've demonstrated." Petra can't help but have a bit of bitterness in her voice.

"You demonstrated it by making that mistake." Byleth corrects, completely tone deaf to Petra's growing anger… or maybe she's just ignoring it. "Now you've learned, yes?"

"Yes…"

"Good." She turns her back and goes back to work. "I'll see you tomorrow morning for stealth training. Dismissed."

###

Despite the confrontation leaving a sour taste in her mouth and in her heart, Petra keeps up her training with the professor. She doesn't stop trying to understand the woman either, though she keeps her emotions are arms length this time. There are still some other parts of Byleth she wants to understand.

"Professor, why do you teach us?"

The woman turns to look at her, with her fake smile affixed to her face as always. "I was hired to."

"Why?"

"Because I have a goddess in my head."

Petra blinks slowly. "Pardon?"

"I was hired because Rhea cares about the goddess in my head." Byleth says with absolute honesty.

"I see." Petra does not see, so she changes tactics. "But why did you grab the job?"

"Take, not grab." Byleth corrects. "But… I took it because I had nothing better to do. My father was forced back into being the captain of the knights of Seiros, and so when I was offered a teaching position I took it simply to have something to do and make money."

"That's very cold professor."

"I'm a mercenary and an assassin, did you expect otherwise?" She asks with a raised eyebrow. "Besides, my view has changed over the months I have been here."

"How so?"

"I care now, about you students, whereas before I saw you as a means to make money." Her smile shifts almost imperceptibly down a fraction, closer to a frown. "It is an objectively poor decision on my part to care. I am too human for my own good, unfortunately."

Petra frowns. "Not long ago you told me you did not care for us, why has your heart altered?"

"I said I didn't trust you." Byleth corrects. "Do not mistake trust and care Petra. You can care for someone without trusting them, and trust someone without caring for them. An assassin, ideally, doesn't care for or trust anyone, but care is much harder to be rid of than trust. Trust is logical, care is emotional. Emotions are always problematic."

"That is no way to live Professor." Petra retorts. "To live without emotion is to not live."

"It's the best way to live." Byleth disagrees. "If you never trust and never care, you are never hurt, never betrayed, and you never lose. You are always prepared for even the most drastic change because you expect nothing and are prepared for everything."

"You are also never happy."

"Not true. Emotions are problematic, but they can be acceptable in a controlled environment."

"You are going back on your own words Professor." Petra frowns. "Does your poor flirting count as controlled?"

Byleth's lips thin almost imperceptibly. Petra can see it though. She's getting under the older woman's skin a bit. Petra doesn't consider herself petty, but she can't deny some vengeful joy at seeing the woman annoyed. "Yes."

"But how could you be considering a relationship if you do not trust?" Petra presses. "That is quite unfair to the other person Professor."

"I- hmm…" The woman blinks. Her fake smile fades into a frown. It's the first time Petra can remembering seeing a different expression on her teacher's face. "That's a fair point."

"Is it not?" Petra nods. "I say this not to be rude Professor, but I think your views may need change. They seem… to be problems."

"'Need to be changed' and 'problematic'." Byleth corrects in a murmur. "But… hmm… maybe." She turns her back. "I'm cancelling our private lesson tonight."

"Understood. You need to think?"

"I'm getting too easy to read." The woman whispers. Her fake smile slips back onto her face. "Yes. Good day Petra."

"Good day Professor."

###

Byleth honestly never considered the fact that she might be wrong about something. Or, at least, not wrong about anything she took herself to know very well. The first thing she learned from Acrim was to always be absolutely confident in yourself. An unsure assassin is a dead assassin, you need to have full confidence in your skills, your plan, your tools, and your reasons.

Petra seems determined to tear down her confidence, and worse yet it's working. She made a good point. Why does she bother flirting with anyone, badly or otherwise, if she has no intention to trust them? That's one of the pillars of marriage, or so she's heard at least.

She should talk to Jeralt, and probably Acrim too.

It doesn't feel right to think she might have to trust someone aside from her father though. It sounds like an objectively stupid thing to do. You might as well be holding a sign reading: "backstab me!"

That's not the only thing she realized today though. Somehow Petra had gotten the impression that she did not care about her, which is bullshit. Perhaps she should have anticipated that the girl would mess up care with trust, it's an easy mistake to make.

Still, Byleth feels uncomfortable with the idea she may have to be more open about herself with someone. Especially Petra, who she's been teaching to manipulate, sneak up on, and kill people for months at this point. She knows Petra can backstab her with ease.

"You're overthinking this, you'll be fine." Sothis huffs.

"That's easy for you to say. You're immortal. If I get a knife slid between my ribs, I'm gone."

Sothis sighs. "That won't happen. In case you haven't noticed, despite your oddities, many of your students are quite fond of you."

Byleth frown. "It still feels wrong."

"Boo-hoo. You're an adult, deal with it." The goddess says. "By the way, I have another question."

"What?"

"You never did explain why you refused to teach Petra seduction."

"Ah that." She sighs. "I'm not oblivious to the fact that my attempts to flirt don't end well, but my seduction is quite good. I don't want her to end up like that and ruin her chances at romance."

"That's absurd." Sothis snorts. "You're messed up in the romance department from learning seduction too early… and just being generally weird."

"I am not weird."

"Suuuure you're not…"

###

"Petra."

"Ah-! Oh, Professor." The girl breathes. "I did not notice you. You are still beyond my ability to detect."

"Good. I haven't lost my touch." Byleth says. She closes the window behind her and sits down on the bed. "We need to talk."

"I see." Petra says in a voice that makes it clear she expected this to happen at some point. She crosses her legs and waits. "What is it Professor?"

"I don't trust you."

"You've told me such before."

"Yes… so how do I trust people?"

Petra blinks. "I'm not sure that's something that can be taught Professor."

"Ah." The hint of disappointment in Byleth's voice is audible. "I see."

"Perhaps, simply… replicate the behavior of someone interacting with a person they trust." Petra suggests. "Like Annette with Mercedes, or vice-versa."

"I should cook badly or make sweets?"

"Not quite."

"Give someone a nickname?"

"No, not that either."

"Go shopping?"

"No."

"Use magic?"

"No."

"Then what?" Byleth asks, starting to get frustrated.

"I mean how they don't assume the other is trying to kill them, and generally don't suspect their intentions." Petra murmurs.

"Oh." The woman blinks. Byleth already knew that, she was just hoping for an easier way out. "Right, of course. So… don't stab me."

Petra raises an eyebrow in confusion, and then raises the other in shock when the woman leans forward and pulls her into a hug. "O-Oh."

"I presume this isn't what normal people do. Especially not a teacher to a student." Byleth says calmly. "But… this is the best I can do for now, it's what I know how to do, and… I'm trusting you won't use this against me."

Not quite what Petra had in mind, but that works. It's a step. An awkward, probably not technically appropriate step according to monastery rules, but she's not about to hold it against her teacher. Considering her social incompetence, this works fine.

"I won't betray your trust Professor."

"That's the hope…"

Hmm… hmm… eh… I think there's some way this could be done really well, and this chapter isn't it. I think the intent got across, but the execution is… lacking. Too much tell, not enough show, and lacking the usual intimidation that makes this Byleth tick. Still, I'll put this out. I like having this and Peculiar Professor mirror each other, though I think from now on I won't do that. This will be the last mirrored chapter just for the sake of freeing up both to do their own thing in the future.