"Are you excited Merry? If I'm right, I expect the youkai sage will be contacting you tonight."

It was the evening of the same day in which we said goodbye to Mr. Easy. Renko and I had stayed and talked with Sanae for an hour or two longer, then returned home from our office, eaten dinner, cleaned up and prepared our lesson plans for tomorrow. Now it was time for bed. I had just changed into my nightgown and was about to squelch the lamp but Renko was looking up at me with eyes that were wide awake and filled with excitement. She was sitting on top of her futon, which she had laid out beside mine, but she was still fully dressed. Where had her lethargy from earlier today gone, I wondered?

"Why do you say that, Renko?" I asked with a sigh. "You were just saying that this case isn't over yet, weren't you?"

"Because she has to, Merry. We've followed the lead she gave us to its conclusion, but there's more she needs us to do. It stands to reason that she'll have to show up and tell us what that is. This time, I'm gonna stay up and see her for myself."

"Even if she were to appear tonight, I doubt she'd do so if you're here. Last time I saw her I went to bed here and woke up in the office. I don't know if I was sleepwalking or if she gapped me there, but if she doesn't want you to see her, I'm pretty sure you won't, Renko."

"That's no fair, Merry. She should try meeting me at least once. I know what she's up to and that she's the one who's hired us now, so what more could she have to conceal?"

"Don't ask me, Renko. I'm not her."

"Are you sure about that? Everyone says she looks just like you. Maybe she replaced you when I wasn't looking and is sitting in front of me right now. Quick Merry, do something to prove you're really you."

"That's silly. By definition, everything I do is proof that I'm me since I'm the one doing it."

"Yeah, that's a pretty Merry-like response," Renko said with a grin. She was trying to be funny, in her usual, hopelessly awkward way, but I couldn't see the mirth in it just then. My mind was occupied with questions and theories of my own. Doubts that I had pushed out of my own head countless times and nameless fears which I had hidden from for so long they had become like background noise. Now though, with the thought of another visit from Yukari looming over me, I couldn't get the questions to stop circling in my mind. Renko seemed to notice my distraction and looked over at me with with genuine concern. "What's up, Merry?"

I lowered my eyes. I'm not nearly so delusional as my partner is in my opinion, and I certainly try to make a point of taking things at face value and seeing how a situation pans out rather than leaping to wild conclusions. When a possibility occurred to me, I had a habit of asking myself if there was any evidence to support my theory or if it was just something my internal biases were taking as fact. It was a knack they had trained us in back in university in the Scientific Century but it was also a habit that appealed to my own sensibilities. I'm a cautious person by nature, at least when my curiosity doesn't get the better of me. Nonetheless, there was a certain theory that had been plaguing my thoughts for the last few days. Something I couldn't get out of my head no matter how irrational it seemed. It concerned the true identity of the youkai sage, and more directly, it concerned the question of why she would use me of all people to be her go-between to talk to Renko, someone she plainly seemed to not want to interact with directly.

"Are you worried?" Renko continued prodding. "So far all of the youkai sage's requests have been for me to do something even if she delivers them through you, right? I don't think she'd get you to do anything dangerous."

"...I'm not sure about that. To be honest, we still don't really know why we came to Gensokyo in the first place. It could have been the youkai sage's doing, but it might have been something your aunt did too. In that case the sage might not have any connection to us, and just be using us as tools or for her amusement. Even with Mr. Easy, she might have had her own reasons for wanting to save him and only employed us at all because she knew his connection to Sumireko would be difficult for us to ignore. When it comes to other people you can theorize all you like and it doesn't really matter, but if we start believing that every aspect of our own lives is part of some grand plan that's just megalomania, isn't it? Or at least a self-centered sort of determinism?"

"You worry too much, Merry. Of course I'm going to make theories about events concerning our own lives. They're our lives! We have to take them seriously!"

"You don't even know if I'm telling the truth. Neither do I for that matter. The last two times I've seen the youkai sage it was after I had been sleeping. Or trying to, at any rate. Who's to say I didn't just doze off and hallucinate her? Those places where I end up were all close enough at hand that I could have conceivably sleepwalked to them. Unless the youkai sage appears in front of you, you can't be sure these tasks she's assigned us are anything more than my bad dreams."

"We can't assume that. If we did then this mystery would be unsolvable."

"Maybe it is, Renko. Or maybe there wasn't ever a mystery to begin with. I met Sumireko in the past when I gave her that piece of amber. I only had it because you and I found it in the future though -in her room where it had probably been since I gave it to her. It's an impossible loop. The amber doesn't come from anywhere. Something like that can't be expected to obey the laws of cause and effect you would expect it to. It's like a bad sci-fi story right from the beginning."

"Well I wouldn't say it's like a 'bad sci-fi story.' Time paradoxes are classic stuff, Merry."

"They're not real though, Renko! They're fiction! You get the difference, right? Despite all the impossible things we've seen here, there's never been any evidence of any kind that time could flow in any way other than forward. Even Sakuya can't turn back the clock, and neither can Kaguya despite them both having control of some aspects of time. Your aunt and that amber are the only incongruous bits. They don't make any sense. Wouldn't the sensible conclusion be to assume that since those mysteries have been there from the start that everything that came after that wasn't real? What if the whole time that we've been in Gensokyo is a dream? You and I could both be in comas. Maybe there was some sort of toxic mold growing in Sumireko's room that did us in the moment we stepped inside and we've just been wasting away. Maybe you're dead for all I know and all of this has just been in my head."

Renko frowned at me, then flopped forward, allowing herself to fall face first onto my futon, right where I was about to lay down. She rolled over and looked up at me.

"That's boring Merry. What kind of an ending would that be? None of the mysteries get solved, it just ends with 'and then I woke up?' That's terrible. It's like something a kid in elementary school would write. Besides, it doesn't matter anyway. Even if it were true this mystery would still be worth solving. The fact that some parts of it don't make any sense just means that we don't have enough information to fill in the gaps yet. I wish Sumireko would hurry up and get here already, or else that the youkai sage would unleash whatever she's been planning this whole time. If something were to happen then we could just get Sanae to fly us straight to the mastermind behind it and get some answers." She shoved her face into my pillow. "No, I definitely don't like that idea, Merry," she said, muffled by the fluff. "I don't like it one bit. If that's how this all ends and we just wake up back in Sumireko's room when this is all over I'll throw a tantrum." She proceeded to demonstrate by thrashing around on my futon, kicking her legs and pounding her fists into the tatami. To think that this girl was a full-grown adult.

I bent down to grab the edge of my futon and hauled with all my might. Renko spun over and flipped onto the tatami. She groaned dramatically but as she looked up at the ceiling her eyes still held that same utterly baseless confidence that had always been her trademark. My partner is the sort who believes -who has always believed that if she can just gather enough clues, if she can just trigger the right flags, she can reveal the truth. A staggering truth. A truth that puts all previous understandings of the world to shame. A truth to unite and illuminate reality and make the stultifying world which never seemed quite big enough to contain her expansive mind a more interesting place.

Maybe that sort of boundless self-assurance is a required feature for a great detective? It was probably because of that baseless confidence that we had sought out and eventually saved Mr. Easy. It was because of Renko's child-like curiosity and reckless obstinance that the two of us had even gotten to know each other at all. If not for her dogged willingness to pursue and pester me I never would have gotten to know her or joined the hifuu club back in Kyoto. Perhaps, in at least that way, she really had succeeded in making the world a more interesting place. At the very least she had done that much to me.

I wouldn't ever tell her that though.

I took a deep breath and let it out slowly, then scooted Renko out of the way with my foot and laid my futon back down. As I was placing the blankets back on top my eyes fell to the endtable in the corner of the room. Renko had placed Mr. Easy's book there. Neither of us had made any attempt to read it yet. He had said that he had intended to throw his life away and be resurrected as a youkai. Could a book really do something like that? Especially one written by a powerless human?

"Hey Renko?"

"Yeah?"

"What do you think it would take for a human to become a youkai?"

In response to my question Renko sat up, back straight and turned to face me. She looked me straight in the eyes, which was a little unusual for her. Usually those eyes were staring off into some imagined future or boundless delusion. She generally spent little time looking at the real world with all of its annoying inconsistencies, imperfections and boring mundanity. She was a physicist, after all. Hers was a world of beautiful, graceful abstracts. Perfectly imagined and elegant theories, complex though they might be, describing a world where everything moved according to the grand plan of a divine watchmaker. It wasn't reality, but I could understand why she would prefer to look upon a beautiful lie rather than an ugly truth. Now though, her eyes were on me, deep and dark. I saw my face reflected in those eyes, but I wonder what it was that Renko really saw when she looked at me. What were the associations and biases her brain linked together when presented with the stimulus of me looking back at her?

"Well, taking in everything we know about Gensokyo, I think we've found eight answers to that question."

"Eight answers?"

"Or rather eight demonstrative cases. The way I see it, there are three aspects to any individual being we've met here: their physical form, their self-perception, and the way that they're seen by others."

"Oh, I think I get what you're saying. Perception affects reality here and there are all sorts of creatures. So in that case would it be possible for something to be a youkai even if they didn't have a youkai-like body?"

"Exactly. If you have someone where the body, the self-image and the perception of others all say 'this is a human' then obviously that person is a human. That's case one. Similarly, if you have someone where all three of those things say 'that's not a human' then there's no question of that being a youkai. Or a god maybe or a fairy or a ghost. At any rate something that isn't human. That's case two."

"Sure."

"Now let's look at the more complicated examples. Number three is someone who's body is monstrous but their self-perception is human and everyone around them sees them as a human as well."

"You're talking about Keine, aren't you?"

"Exactly. She's unquestionably a were-hakutaku. We've seen her transform, but because she's sure that she's a human and everyone agrees with her she's allowed to live in the village. Through sheer determination she's held on to her humanity. Compare her to example four though. Mokou has an inhuman body, and it's inhuman in such a way that she can't hide her inhumanity from others. Not for very long anyway. As a result, she's considered inhuman by others. Even though she still sees herself as a human there's enough different about her that she can't live in the village. I think that's why she can't ever get over her grudge with Kaguya. Kaguya doesn't think she's a human and she doesn't think Mokou is either. If Mokou were to accept that premise she'd lose the only thing she has left from her original life, her self-perception.

"Alright, I'm following you."

"Then lets move onto the next example. Number five. Someone with the body of a monster and the self-perception of a monster, but who's seen as just a human by everyone around her. That's Sekibanki. Because she's accepted here, she gets to live in the village despite not being a human. Her exact opposite would be example six: Sakuya Izayoi. She has a human body, but I don't think she sees herself as a human. As for everyone else... well anyone who's met her probably wouldn't think of her as a normal human anyway. She can come into town whenever she likes but I think she's weird enough that people wouldn't let her live here, not that she'd ever want to."

"That's probably true. I think if you were to ask her if she were human or not she'd reply that she'd the maid of the Scarlet Devil Mansion."

"Right, so onto examples seven and eight then. Someone who has a human body, but thinks of themselves as something other than human. This would be Sanae and Youmu. Sanae of course would immediately say that she's a living god, not a youkai, but the point remains that she still considers herself to be something other than a normal human. As for perception, I think most people probably think that both of those two are human at first, but the more they get to know them, the less they'd think so. As a result they both fall into the category of people who can come into the village but couldn't live here, unlike Banki, who can get by in the village just fine, despite having a head that comes off."

"So where do those eight examples lead you?"

"Well, if we compare all of them, I think we can start to define the boundary between human and youkai. In order for something to be considered inhuman it has to be inhuman in all three ways that matter. Even Youmu, who sees herself as half-human has enough humanity to her that she's not considered a youkai and is allowed into the village. She gets weird looks when she visits, but no one chases her out."

If Renko's reasoning was correct then becoming a youkai was actually a pretty high bar to clear. High enough that I don't see why Reimu would be worried about us crossing the line accidentally. There were two more cases that also stood out to me after hearing that. Reimu definitely considered Byakuren and the crown prince to both be youkai, but I wonder if they themselves did? Certainly they both seemed to be able to come into town quite extensively and I had never felt the predatory sense of otherness the accompanied most youkai from either of them. I had thought up until now that that had been a result of each of them suppressing their youkai auras in order to gather faith, but maybe it was simply a part of their nature.

"So in that case, if a creature were born as a youkai, even if they saw themselves as human and were perceived by others as human, they could never become a human, right? Ultimately they'd still have the body of a youkai."

"I wonder about that. There are lots of stories about foxes falling in love with humans and eventually becoming one after learning to shapeshift. I'm not sure how that works because we don't have any clear examples, but it seems to suggest that if a being could either change their body or throw it away and take a new one, then such things could be possible." Renko shrugged her shoulders then let out a long yawn.

"Just change into your pajamas and go to bed already, Renko. It's late and we have classes to teach in the morning."

She snorted at me and scowled in frustration. "You're going to run off with the youkai sage and have interesting adventures as soon as I do. Maybe I should change my name to Merry, then she'd come and visit me."

"Maybe that's exactly what she wants you to do, Renko. Your whole life is just part of her master plan, right?"

"Are you on her side, Merry? Are you just trying to lull me to sleep so you can sneak away with her?"

I shook my head. "Get changed, Renko. I'm going to go brush my teeth and when I come back I'm turning off the light."

I went and did that and when I came back, I was mildly surprised to find that she had listened to me and was laying in her own futon. As I put the snuffer to the lamp another question crossed my mind. "Hey Renko?" I asked over the sputter of the wick. "If you were given the choice between remaining a human and becoming a youkai right now, which would you choose?"

"I have to pick right now?" The darkness asked me as I settled into my futon, "and I assume I don't get to go back once I've made my choice, right?"

"That's right. No take-backs."

I couldn't see anything in our dark little room now, but I heard the sound of her moving about, then the fabric of the futon moved beneath me as she snuggled over onto my bedding. Outside of the window of our room the moon was shining, but as my eyes hadn't adjusted yet it simply looked like white on black. I couldn't make out any expression or get any hint as to what might be going through her mind. But when she laid her hand gently against my cheek, somehow I knew that she was smiling like the Cheshire cat.

"Then I'd do whatever you were going to do, Merry. I'd want to stay with you."