Best friends were quite funny things.

Hands down, I was Rosa's best friend and Rosa was my best friend. She was practically a sister to me. I would support her in all her endeavors (as long as they were sane), I would cheer her on for all of her life (as long as she was sane), and I would maybe even die for her. ...Probably. As long as it was something actually dangerous, and not something like Filly, try die for me so I can calculate the rate that death takes over a person.

...okay, so maybe I wasn't the best friend someone could have, but still! The point here was, I could give up a whole lot for this girl, but I drew the line at sitting in on one of her very long and very winded lectures after a long day of work.

Which was why, three minutes into her lecture, I began closing up the restaurant as speedily as possible.

Cook came in with a frown at the noise, his mouth half-open (probably to tell Rosa or me off), took one look at the two kneeling and miserable loan sharks and Rosa drawing out a graph onto some kind of board she brought from who-knows-where, and sighed. He then turned to me, his eyebrows raised as if to say, what are you going to do with that girl?

I shrugged. Nothing. I was going to go home and sleep.

"Now, if we take a brief detour into thinking about this graph by itself, and attempt to approximate the slope for this hyperbolic function, we would have to take the standard formula y=mx² and make it negative, because it's an inverted hyperbola. Since we're starting our y-axis right here..."

Yup, I was done.

And you know what? Rosa couldn't have chosen a better revenge for me. The two loan sharks were looking incredibly, dead. No, really-- any speck of light that may have ever existed in those two pairs of eyes were now as extinguished as they could ever be. I snorted. I didn't envy them.

"I take back taking back my take back," I whispered, then waved bye! to Rosa and quietly headed to the stairs.

Simon must've heard the rustles behind him-- he twisted around and gave me a baleful glare, as if he couldn't believe I was jumping ship. 

I shrugged.

"Focus!" barked Rosa, and the lanky, tall, tattooed loan shark miserably turned back and hung his head.

Biting back a mean snicker, I gently closed the door behind me. Then I frowned. Hadn't, hadn't Rosa said she needed to tell me something?

I considered going back there to ask her about it, then changed my mind. Better not risk it-- I could get caught by her in her mathematical throes, too, and be forced to listen until she finished. Shuddering, I dragged my aching feet up the stairs.

"Eh, she can tell me tomorrow," I murmured, then collapsed onto the bed face down.

---

The next day, an hour before my dinner shift began, Rosa popped in.

"Hi Filly!" she said cheerfully, strolling towards me.

I set down the fork I was polishing and frowned. "Are you okay?"

"Hmm? Yeah, why?"

I regarded her carefully, shifting my weight to my other leg. "I don't know, you seem... nervous?"

She paused, but shook her head brightly. "You're imagining things."

"...sure," I said slowly, not convinced. "Anyways, what were you going to tell me yesterday?"

"Right. That's what I'm here to talk to you about." She came and sat at the table across me, took a deep breath, and looked up at me straight in the eye. "Filian," she said, her tone serious, the gold of her eyes flashing, "I'm going to tell you something, but I want you to listen to the very end, okay?"

I raised an eyebrow as I took up the fork and rag again. "Go on."

"And don't judge."

"Okay."

"And I'm not going insane, so don't think about that either."

"Okay. Go on."

"And--"

I threw up a hand. "I get it. I won't judge you, I won't think you're insane, and I'll listen to the very end. I'll do my best to understand you, okay?"

Rosa exhaled. "Okay." She bit her lip, still tense. "I don't know how to tell you this and you know how bad I am at being subtle, so I'm going to just tell it to you straight."

"I'm listening."

She squared her shoulders, then looked up at me with a smile that was so obviously fake that I would've commented on it if not for the very next words that came out of her mouth. "I'm actually not Rosa."

I blinked. Huh? What did that mean?

"I mean, I am Rosa. I'm Rosa in this world, but originally I wasn't her. It's like, this body-- this life-- this figure called 'Rosa' is like x, an empty function. It has the possibility to be any number. And I, a random number, am defining it in this life."

Ex? Numbers? What?

She rushed on, her words tumbling out of her mouth over each other. "In other words, this figure called Rosa existed separately from the figure I was originally, and when the figure I used to be died, I was re-assigned to Rosa. I think that's what happened, yeah. And so now I am Rosa, but I originally was not."

I swallowed, not even noticing that I hadn't been polishing for the entire time Rosa was talking. My head swirled in circles, trying to make sense of what she was saying. "Wait, explain it to me again. So you're Rosa now, but you... aren't?"

Rosa nodded, her golden eyes flickering anxiously. "I don't know exactly how it happened or what happened, but I think Rosa didn't have an actual definition to it-- it was just an empty shell-- and I came to fill it, or something."

I set down the fork again, without really meaning to. "What does that mean, though?"

"I mean, 'Rosa'-- that is, this person called Rosa, not who's in her, which is me-- egh." She sighed in frustration. "This is hard to explain. Umm... Let's say there's an outer person and an inner person. Rosa's the outer person, and she did not have an inner person. I had a different outer person, but now I am the inner person inside Rosa the outer person. Does that make more sense?"

"No," I said slowly, "but let me think."

We stayed silent for a little while as I tried to process what she was saying. "So... inner person. Like, the soul?"

Rosa perked up. "Yes! So my soul came into Rosa's body once my original body died."

I rocked back and forth on the balls of my feet, my thoughts whirring noisily in my head. I knew Rosa had told me to listen to her until the very end and not judge her or think she was going insane, but this was... well, this was not what I'd been expecting. I thought she was going to, I don't know, 'fess up to something horrible she'd done to me. Or something. Not announce she wasn't Rosa.

If she wasn't Rosa, who was she?

Putting aside my own complicated feelings about all this, I refocused on Rosa. "Then... whose body were you in originally?"

"Mine," she supplied helpfully.

I shook my head. "I'm asking, who are you then? If your soul is not Rosa?"

"Ohh. My name... was Kawahara Sumie." A strange expression crossed her face, and she tried to smile. "This is so weird. I haven't thought of that name in so long."

"I used to live in a word that's so different from ours--" she stopped for a second, then forced herself to continue. "Yes. So different from this world. We had skyscrapers, wifi, phones, and games. I lived in a place called Japan, and I had black hair and brown eyes. We all did, over there-- my whole family. I used to have an older sister I loved to hate, you know." She barked out a laugh. "Now I'm the oldest sister."

Her head drooped slightly and fell silent, and we stayed like that for a while, letting the silence envelope us as I watched her thoughtfully.

"So that's why," I said, my voice quiet.

Rosa blinked, her yellow eyes coming up to meet mine again. "What?"

"You know, you used to get this look in your eyes." I nodded at her. "You had that look again."

"That look?" she repeated faintly.

"Yeah, when you look like the saddest person in the world."

A flash of surprise passed through her eyes, but then it was quickly replaced with the most painful expression I had ever seen from her.

She stared at me, and I stared at her, and in her eyes I read hopelessness and crushing defeat, and a searing, burning pain that took my breath away.

I had ever seen her look of pain in tiny slips, the smallest passing expressions-- but faced with it entirely, the brunt of it was so strong that I felt like someone had physically hit me. The rag in my hand slipped off as I lost the strength in my arms, and I sat down hard on the stool beneath me.

"Oh, Rosa," I whispered hoarsely. I felt absolutely helpless, and tears welled up in my eyes. I wiped at them angrily-- I hated how quickly I cried at times like this.

As I wiped tears away with the back of my hands, Rosa's low chuckle that followed it was the most bitter I'd ever heard her to be. She gently patted me as I clenched my teeth. "Don't worry about it, Fi. It's not something you can do anything about." She shrugged. "It's not something I can do anything about either. Besides, it's been years. I'll be fine."

But as she said that, I realized for the first time that some people-- people who were in pain for so long, who had no way to get rid of the pain that buried itself permanently into the depths of their heart, people like Rosa-- smiled when they could cry no longer, and that those smiles were the most heartbreaking things you could ever see.