"You're a natural with weapons," Cyne told Rina as they exited the Guild's training area.
"Really?"
"Yeah. Compared to Iris, your skill is like night and day, to the point I have trouble believing you've never handled a sword before. With your agility and your strength, you'd be particularly compatible with a heavy weapon."
"Like... A spear?"
"I could see you with one! How about we do that next time? I can teach you the basics."

Rina nodded eagerly at this suggestion, and her ears perked up when she heard a familiar voice a good distance away.

"Is something wrong?"
"Mmh. Iris is back. I'll go see her," she replied, already on her way.

***

"Ah, perfect timing, Rina!" Iris said cheerfully. "We just received a response from your former branch of the Guild. The transfer has been done, so you're now officially an adventurer assigned to this branch! Congrats!"

The beast girl beamed. Because she was not affiliated with this branch until now, she had not been able to partake in E-ranked missions from here and had to be taken in charge by Iris and Cyne for a couple of days since she had come here. Now that she was officially registered as an E-rank adventurer, however, she was looking forward to start paying back the lodging.

"In their letter, the other branch also asked if you wanted the rest of your belongings to be brought here by carriage," the clerk girl added.
"... That service is expensive, isn't it? I... I don't need what I left there."
"Don't say that," Iris protested. "Whether or not they're useful, they're still your things. I'll pay."
"I-if you do, I won't be able to repay you..."
"As I said many times, you don't need to," Iris sighed. "I pretty much forced you to come with us in a hurry without taking anything with you, so I'll take responsibility for this as well."
"... Thank you."
"You're lucky to have found those two, Rina," mused Melisandre. "From what I heard, if not for Iris and Cyne, you could have been enslaved or even killed."
"Yes! Iris saved my life during the fight!"
"Please don't sugarcoat it... It was more of a miracle than a save," Iris clarified. "The fact that my mana was there at that time was a pure coincidence." 
"A miracle, huh?" Melisandre began, "As you know, Iris, I had my doubts about your collaboration with Cyne at first. When it leads to saving many lives, though, I can hardly complain. Perhaps you two were fated to meet and save that girl, after all."
"Fate...?" the beastfolk whispered as she pondered the idea.
"I didn't expect you to believe in these kinds of things, Melis. Then again, I suppose astrology is popular among women..."
"You'd be surprised by the insights stars can give about your life and your future."

(Yeah... Another victim of the Barnum effect. I just hope she doesn't convert Rina.)

"Well," Iris said dryly, "I'm still waiting to see what future Phaethon has prepared for me."
"... Considering your birthday, that's not the right constellation. Wouldn't it be Aesteria instead?"
"I know, right?" she shrugged. "In any case, you can accept the offer for her luggage."

***

"Is the food not to your liking, Rina?" Iris asked as she noticed that the beast girl had barely touched her plate.
"You're clearly malnourished, so you should eat," Cyne added. "It's the one thing limiting your strength right now."
"... It's not that. The food is good. I... I've been thinking about what the receptionist said earlier."
"... About your luggage?"
"No, not that," Rina replied, shaking her head. "... About Destiny," she continued with an intense expression.

(Crap. I was too late. She's already been converted by Melis' nonsense.)

"... What about Destiny?" Cyne frowned.
"What if we were fated to meet? I considered everything that happened. The fact that my abductors tried their luck on you. The fact that, despite a clear disadvantage, you chose to fight. The fact that my magic protected me at the best possible time by pure coincidence. Add to that the fact that my mana veins have been activated by the only person able to and willing to help my condition that could kill me in days. Doesn't it feel somehow... preordained?"

Iris was stunned by the passion and intensity in the speech of Rina, who she had thought wasn't particularly talkative before now.

(This sudden change of life must have been hard on her. It's clear that she's trying her best to find a grand reason that could give meaning to what she's going through. Beastfolks usually don't believe in gods, so Rina must have settled down on believing in Fate instead.) 

Seeing Iris and Cyne glancing at each other without saying a thing, Rina returned to being a bit more bashful. "You... don't believe so?"
"I don't," Cyne began, searching for the right words. "I don't believe in such a thing as Destiny. I'd even say that I've spent a good portion of my life trying to disprove this concept. I was originally 'fated' to lead a clinic in Phesiora and follow my father's footsteps and yet, I went against this destiny to do something else entirely. Isn't that proof that it doesn't exist?"
For a bit, Rina was searching for a counter-argument, and she grinned when she managed to find one. "How can you be sure that your fate was to lead a clinic and that you changed it? For all you know, Destiny might have planned for you to become an adventurer all along."
Cyne grimaced. "Uh..." 
"Pfft-!" Iris puffed.

Irritated at being laughed at by little girls after sharing his very personal viewpoint, Cyne shot Iris a withering look.

"Ah. It's just that... Rina said almost exactly the same thing as... someone I know," Iris said as her eyes grew more distant and her voice softened ever-so-slightly. "Fate, huh? In a way, that might not be wrong."
"So you believe in those things too..."
"I don't in a superstitious way. From a purely scientific point of view, however, this concept is interesting."
"How is that scientific?"
"Let me ask you a question. Does the future already exist?"
"What?"
"This question might sound stupid, but it's not. You might see space and time as two separate concepts, but they're in fact interconnected and part of the same fabric called spacetime."
"... Did you just combine two words together and pretend it's a new one?" Cyne asked, visibly unimpressed.
"N-no, I... I mean... I suppose it's not a very thought-out name, but I'm not the one who came up with the term... Anyway," Iris cleared her throat, "With this interpretation, spacetime is a four-dimensional manifold. Every event happening can be described by three spatial coordinates and another that will inform of its location in time. Said in another way, the four coordinates tell us where the event occurs in spacetime."
"Sounds speculative. What's your point?"
"Speculative...? The theories of Relativity are some of the most validated ones in the entire universe."

(Well, based on a sample of two worlds. General and Special Relativity have predicted quite a number of things like gravitational waves, gravitational lensing, and time dilation. Even the strangeness of the perihelion procession of Mercury has been solved.)

"As for my point, it's quite simple, really. This discussion we're having occurs somewhere in spacetime, while every future conversation that will happen around the table we're at is located somewhere else in spacetime. In a way, those future events are already a thing in this four-dimensional fabric. They're just currently inaccessible since we can't freely move in time."

Iris glanced at Rina who had started this, and she seemed confused. Either she didn't grasp where Iris was going with her explanation, or she gave up at the first mention of spacetime.

"This is the foundation of the Block Universe view, also called Eternalism. Past events are still somewhere in spacetime at coordinates we'll never be able to access ever again. The future already exists somewhere in spacetime, and we'll gain access to it simply by waiting and thus moving slowly forward in time. If the future is already a thing, it can't change in any way. Isn't the notion of a predetermined and immutable future similar to what you would call Destiny?"
"I'm not sure you can just say the past, present and future are the same thing..."
"Special Relativity states they are," continued Iris. "The notion of 'now' makes little sense because a causal chain of events can occur in a different order depending on the observer. There is no preferred referential, so all the different points of view are correct. Yesterday or tomorrow isn't particularly less real than today."
"And... you lost me here."
"This is quite mind-boggling, isn't it? I was a bit like you the first time I heard this, but it also hooked me at the same time. Maybe this will be the case for you too."
"Nah. I'm not convinced by your explanation."
"I see."

(That's too bad, but I suppose not everyone can adhere to the perspective Relativity offers.)

"In any case, I'm not saying this view is necessarily correct. I'm not quite sure I believe in it myself. After all, it's contradictory to another theory that is as well-established as Relativity, called Quantum Mechanics. If I had to summarize the quantum view on this subject, it would be that there exists an intrinsic unpredictability in the state of matter at scales even smaller than you can imagine. The way particles acquire their states doesn't seem to be determined in advance by hidden variables. There is also entanglement, referred to as a 'spooky action at a distance', that causes a sort of simultaneity regardless of the distance, which is at odds with Special Relativity."
""...""

(W-was that too much in one go?)

"Uh... Anyway, that's the scientific caution of Presentism, the view that states that the future isn't immutable and even that only the present exists," Iris started to conclude, but her passion got the better of her. "Additionally, some strange interpretations of Quantum Mechanics make things even weirder by challenging causality. Retrocausality, for instance, might be a case where the collapse of a wave function retroactively alters the past so that an entangled particle 'knows' in which state it should collapse beforehand."
""...""

(Oh. Did I do it again?)

"... Forget about that last part. It's very speculative."
"The whole thing sounds speculative and incomprehensible," Cyne said.
"R-really? I dumbed it down though... Maybe I'm not the best teacher?"
"Did you actually expect us to follow...?" he asked, amazed by how disconnected elves were from human culture.

(But Maximilian seemed to understand when I taught him things like that... He was even nodding from time to time. Wait, was he tricking me?!)

"Iris," Rina began, "... How come you know these things when we're around the same age?"
"She's a bit older than she looks," Cyne said with the proud look of someone who knew about Iris' real identity, which made Iris tense up.

(Don't make it obvious...)

Considering her sense of smell, Iris reckoned Rina was probably aware that she was a normal human.

"I... I owe all this knowledge to that person I briefly mentioned earlier. You could say she was my teacher."

(Well, it's more like I watched my 'teacher' get taught in my sleep.)

"So, you've had access to tutoring, huh?" Cyne said. "How about you introduce me? I would rather hear this from someone whose job it is to teach."
"I... can't do that. She passed away."
"Ah... I'm sorry for being inconsiderate."
"It's alright, it was a long time ago. I might be inexperienced in teaching these things, but I feel compelled to share that knowledge in some form. Maybe I'm doing it for her."

Iris glanced around and noticed she had dampened the mood with her overly melancholic tone.

"... In any case, if we're all truly destined to end up together, our paths will surely converge in time," she smiled mysteriously.
Cyne snorted. "Yeah, well, I'm quitting this party when I become C-rank."
Iris shot him a look. "Y-you ruined the atmosphere I was looking for!"
"Just keeping it real."
"Uh..."
"Is this relativity thing the reason you wanted to give that name to this party, anyway?"
"... That's right. 'The Relativists' should make more sense now that you get the gist of it. Do you like it?"
"I'll let you make the final choice as the leader. As for me, I wouldn't say I like it. It doesn't even describe any of our skills."
Iris glanced at the beast girl, who had at some point resumed eating her food, "I... wonder about that."