Feh, that's so annoying.
Yet, it ends up happening anyway, by order of your group leader.

You and Meimona rearrange everything, leaving only a tight squeeze behind the last bookshelf, just wide enough for each of you to sneak back into the tunnel. Now, no one should be able to follow your tracks. Therefore...

There's no reason for him to disregard suggestions of Destruction now.

Reed: Confirm rift direction.

Nino: Let me guess, the path we're supposed to take is...
Reed: Yep. Right behind that big gate.
Nino: Aaaand it's locked. Go figure.
Aria: Try the key you got, Mei!
Meimona: Uhm, it doesn't fit into this lock.
Nino: So it's a key for something else, then.
Five: Gasp! Maybe... another treasure chest!?
Meimona: I sure hope so! It'd be so boring if it just opened some door.
Aria: But that's the most useful thing it could do for us right now... ^^;

Meimona: Check under the rug! There might be treasure hidden!

Meimona: Buh, there's nothing here.
Nino: Whoa, don't crawl under the carpet!
Reed: What are you, a rat?
Meimona: Hey- you're the ones who said to check under the rugs!
Aria: You don't have to do it like that though, do you?
Five: But... it looks kind of fun! Like hide-and-seek!
Meimona: PTHHHHHHGPHPPHTTHHFFFFFFFTH, eeeuugh! I got dirt in my mouth!
Five: ...Oh.
Nino: Aaaand that's why you don't wanna imitate this, Five.
Aria: Try to be a better role model for her, will you...

Nino: Pose in the center of that rug pattern.

Nino: Hm. Hmmm.
Aria: Uh... what are you doing?
Nino: Checking if standing here would do anything.
Nino: I guess not, huh!
Reed: What exactly were you expecting that to do.
Nino: I dunno, just trying the obvious solution, really!
Nino: 'cause there's clearly yet another puzzle we have to figure out in here.
Aria: ...Are the poses part of the solution, too?
Nino: No! Posing is just WAYYYY cooler than standing still.
Aria: Is that so...
Meimona: And YOU call ME ridiculous, huh. >:I

Aria: Inspect wall-patterns.

Aria: Well, if we're looking for clues around the place again,
Aria: The patterns here stick out the most.
Meimona: Ooh, this looks like stained glass! Pretty!
Aria: I'm not sure what to do with it, or what it means right now...
Aria: But I'll take note of it, just in case!
Reed: ...Need a picture? I can snap one real quick.
Nino: Oh, excellent idea, actually!
Aria: Yes! Please do, Reed. :D
Meimona: Sooooo, since nothing here does anything so far,
Meimona: How's about we go check out the other rooms now?
Meimona: Maybe we'll find the TREASURE my key opens!
Nino: Yeah, let's have a look. Uhh...
Nino: Wanna check the room on the left first, guys?
Reed: Don't make a difference to me where we go.
Aria: We'll take whichever way you pick, Nino!
Nino: ...Left side it is, then!
Meimona: Aye aye, captain. :]

Meimona: You gotta check the other rooms for TREASURE!

Meimona: Wuh, this room is so... vertical.
Meimona: And I don't see any treasure chests here. :[
Five: Treasure, treasure, where are you hiding...
Reed: There's nothing notable at the top floor.
Nino: You sure? What's that on the wall up there?
Reed: Looks like an unlit torch.
Reed: I didn't think it was important enough to mention.
Reed: Does it actually matter?
Nino: Uhhh, maybe? Or maybe not...?
Aria: The middle floor is empty, besides some sofas.
Aria: And there's also this, um, huge mural, on the ground?
Five: Whoa! It looks like... a big eye!
Meimona: With a rhombus for a pupil! Freaky!!!
Nino: Huh. This an interesting design to find here of all places.
Aria: Yeah... diamonds are the universal symbol of humankind, aren't they?
Meimona: Then what's this doing in the monster world!?
Reed: It's not just the diamond, though. It's the eye.
Reed: It looks similar to the eyes of the human royal family.
Aria: Huh? Their eyes have, um... a diamond in the pupil?
Reed: Oh. You don't know this, do you.
Reed: The human prince, Ruit. There's something unique about his eyes.
Reed: When light hits them, they shine with a diamond-shaped glint.
Reed: It's so distinctive that you just can't miss it.
Nino: Whoa, so this isn't just about humans in general...
Nino: It's specifically related to the current prince?
Reed: That, or the royal bloodline as a whole.
Reed: I think it's genetic to have eyes like these.
Meimona: Oooh, I know!
Meimona: I bet the room on the other side is gonna have another eye...
Meimona: And it's gonna reference monsterkind instead!
Aria: Whoa... parallels!
Nino: Well, this is fascinating and all, but...
Nino: I am wondering what the heck this clue could even mean for us.
Reed: That's if it actually is a clue, and not just some random artistic thing.
Meimona: C'mon, let's check the other room! I wanna see if I'm right!!!
Meimona: They're totally gonna be mirrors of each other!

Party: Go on, then.

You enter the room on the right.
It's another near-identical layout as Mei predicted!

With one obvious difference, of course.

Nino: That looks like a crescent inside the pupil.
Meimona: Uuumm, Aria? Does the monster prince have eyes like these?
Aria: No! And I don't know any monster who does, really...
Aria: I've never heard of the royal family having unique pupils at all, either.
Nino: Huh, so is that phenomenon unique to humankind's royal family?
Aria: Most likely so! The concept of a unique pupil shapes is foreign to me.
Aria: I'm only familiar with pupil color differences, really.
Meimona: Well in that case, the heck does this crescent-eye mean!?
Nino: Just another thing from the human world, maybe?
Meimona: How about it, Reed?
Reed: Couldn't tell you.
Reed: Never heard of a crescent-shape appearing in anyone's pupil before.
Reed: But, I only know about the diamond-eye because of how prominent it is.
Reed: Like, every time you check the news and see the prince,
Reed: You immediately notice how different it looks, y'know?
Reed: So this other pupil shape could just be too obscure for me to encounter.
Meimona: Nooo, not like this... our parallels theory is falling apart fast...
Aria: You were right that the rooms would be mirrored, though!
Aria: That has to be relevant again, just like the rooms with the bookshelves!
Nino: So, maybe something we do on this side will change something on the other?
Aria: There has to be something we can do to open up the locked gate, too.
Meimona: I bet the solution to whatever puzzle is in here reveals the key for it!

---->

Reed: Okay then. Any ideas on what we should try?

Nino: Uhh... maybe there's something to do with the murals?

Reed: Eh. Don't let the eye stuff distract you, I say.

Reed: It's probably just some sort of bold design choice.

Aria: Probably. But it does remind me of something.

Aria: While I can't think as if I'm in a video game like you do...

Aria: I do get the idea of this being some sort of security mechanism.

Aria: And to me, the best method to hide anything would be an illusion.

Aria: You know - something that's meant to fool your eyes?

Nino: Oooooh!

Meimona: Woooow!

Reed: Ah.

Aria: So I've been looking around for anything like that. For example, fake illusory walls!

Aria: But so far, um...

Aria: Check for illusions! Maybe a secret door is hidden somewhere?

Aria: There doesn't seem to be anything of the sort here, unfortunately.
Aria: As far as I can tell, anyhow... haha. ^^;
Meimona: Aw, maaaan! I got my hopes up for nothing!
Meimona: I was hoping you would get to show off a lil', Aria...
Nino: I appreciate that someone had a non-destructive idea, for once.
Nino: But, Aria, how sure are you that there's no illusory tricks at play?
Aria: VERY sure. I think I'd have noticed by now if there was anything big going on.
Aria: Ludwig's also decently good at sniffing illusions out, too!
Meimona: Sooo, judging by the fact that big L's been chilling this whole time...
Aria: Nothing so far sets off his doggy alarm, yep!
Reed: ...Hey. You think we can use her here?
Reed: The uh, spirit.
Aria: Ah, you mean Sintheia?
Meimona: Use the actual name you gave her, dummy.
Nino: Oh, a spirit might be able to notice subtle illusions better than us!
Aria: Um... I'm not bad at noticing illusions, you know.
Nino: That's not what I meant! However good you are at that...
Nino: A spirit is probably just NATURALLY better anyway, yeah?
Aria: Well, maybe. I did beat her in a battle of illusions, though!
Nino: Are you seriously getting offended by that, Aria...
Meimona: Ooooooh, can Sintheia phase through walls, Reed?
Five: Gasp! Like a ghoooost...?
Reed: That's actually exactly what I'm thinking of.
Reed: She could help us find secret entrances that way.
Aria: Ohh, I see... yeah, Ludwig can't do that much, unfortunately.
Aria: But a spirit might just be intangible enough for the job.
Meimona: What are we waiting for, then? Get her in here!
Nino: But how? Is she going to show up if we call her name or something?
Aria: If Reed does, then yeah, supposedly she will answer.
Reed: ...Supposedly. But I'm not sure it'll work now.
Reed: You did send her away and all.
Nino: Huh!? What do you mean, sent her away?
Meimona: Now why in the world would you do that!
Nino: Seems like a total waste of her usefulness...
Nino: Were you just jealous or something?
Aria: What the- no, I was not! Why would I be!?
Meimona: And you're only telling us about this NOW?
Aria: I was going to tell you - once she's with us again!
Aria: It's not like she won't ever be back, so calm down...

Aria: Confirm status of spirit ally.

Aria: I only ordered her to go see her master for a bit.
Nino: The same person who sent her after us in the first place?
Meimona: Why the heck did you do that!?
Aria: Oh, it isn't like doing that will set her free.
Aria: I just wanted her to deliver an important message, really!
Nino: A... message? About what, exactly?
Aria: I told her...

Aria: Issue COMMAND.

"When you see your former master again,"
"Tell her that she is a huge COWARD!"

Nino: W...what the... so you...
Nino: You basically provoked them even more.
Meimona: W-why in the world would you do THAT!?
Aria: Why not? I'm not afraid of whoever her master is. Are you?
Aria: If all she can afford to send after us are these flimsy spirits,
Aria: Then she's definitely just some weak coward!
Nino: I'm surprised that Reed really just let that happen...
Reed: Oh, no. I was just as taken aback as you are now.
Reed: But, judging by the fact that no people came after us,
Reed: Say, royal guards or something like that...
Reed: I concluded that this must be the work of someone without strong forces under their command, too weak to confront us head-on themselves.
Reed: If it were anyone with real power,
Reed: I think we'd have been swarmed by royal guards and detained hours ago.
Meimona: So that's why Aria's not scared at all...
Aria: Their master will be satisfied if we just leave this world, anyway.
Aria: Her spirits won't be coming after us as long as we're doing just that!
Meimona: Wow, um... I guess that's okay, then?
Aria: Hold your head high, Mei! There's nothing to be scared of.
Aria: We've made it this far, after all.
Nino: Well, the fact that we did come this far despite everything they've tried against us was probably going to communicate the same message, sooner or later.
Nino: I just hope you didn't draw unnecessary fire to yourself with that.
Aria: Whoa! That's almost verbatim the same thing Reed said to me about it!
Aria: But it's okay. To be honest...
Aria: I'd rather that master come confront us directly if she has a problem with us,
Aria: Instead of hiding behind even more spirits.
Aria: I'm sure I could best her in a fight if she's THAT cowardly!
Nino: Since when were you so bloodthirsty...?

Reed: Call out to Sintheia.

Reed: ...Well, what's done is done. Somehow, there's no stopping Aria once she takes charge.

Nino: The fact that you're the one saying that sure is something.

Reed: The spirit's still obligated to respond to us, so there's that at least.

Meimona: I-it's okay! None of it will matter once we're home! Even if the spirits' master herself chases us...

Aria: Oh, come on. I'm absolutely sure that woman is nothing to be afraid of.

Aria: But don't worry. I'll take responsibility and rip her to shreds by myself, if needed.

Meimona: W-well actually, methinks it's definitely too late for anyone to come after us now...

Nino: Right... let's focus on what we can do to progress instead.

Nino: Reed, try getting Sintheia in here to help us out a little, will you?

Nino: It's your leader's orders! Chop chop.

Reed: Fine. I'm giving it a shot just to get you off my case.

---->

Reed: Uh... ahem.
Reed: Hey?
Reed: Sintheia?
Reed: Can you hear me?
Aria: ...Nothing's happening.
Meimona: You have to do it louder, Reed!
Nino: Yeah, try harder, dude!
Reed: No. This feels incredibly stupid.
Meimona: Aaaw, man. You're giving up waayyyy too early.
Nino: Dude, are your lungs too rotted to scream or something?
Aria: Are you guys just messing with him? That's not nice...
Meimona: Am not! A summoning HAS to look way flashier than this!
Meimona: He shouldn't be giving us this talking-into-a-phone energy at aaaall!
Nino: Yeah! C'mon, put some heart into it, Reed!
Reed: ...Fine. You guys want loud?
Reed: I can be loud.