So, I had a theory for Kyrietrice that involved Genji in her murder plot against the cousins and Rosa, but found it failed spectacularly because of this one red about Genji: Genji never left the mansion after 24:00, so Genji could not have escorted the cousins out of the cousins' room in the guesthouse after 24:00, and no other party could get to said cousins in time. I thought it was completely impossible for Kyrie now, but then I saw this red:

During the short break at 1:00 AM, the first two to leave the dining hall were Rosa and Eva. Until Eva returned, everyone in the dining hall remained there. After seeing Rosa off, Eva went to the waiting room and sealed it. Of course, she did not enter the room at all at this time.

These two underlined parts bear important meaning. First of all, Eva and Rosa were the first two to leave, and nobody else left the dining hall for the 1:00 AM break until Eva returned. But nobody said it was impossible for somebody like Kyrie to leave the mansion after Eva got back.

Now, I know what you're thinking: Erika sealed all the windows in the guesthouse from the outside, so the cousin room murders are impossible for Kyrie. But...are they, truly? Let's examine the reds about this:

It is impossible for someone to reach the second floor of the guesthouse without anyone in the lounge noticing it. ...Though of course, this only refers to reaching the second floor from inside the building.

It was impossible to reach the second floor of the guesthouse without passing through the lounge, and impossible to reach it at all without Erika, who was in the lounge, knowing about it!

Lady Erika's lookout in the lounge was perfect.There were no small gaps or carelessness or times when she looked away for even a second.

Therefore, during their entire meeting in the lounge, only Rosa went up to the second floor!

It is impossible to tear off any of the seals by any method without leaving marks.

There were no suspicious marks on any of the seals...!

Now, that second red truth seems to nullify it completely, right? Weeeell...not entirely, actually. Allow me to give some expansion. Erika likely put seals on the window from the outside as well as a seal on everybody's doors in the guesthouse after they entered them. She does this with Kumasawa to lock her in her room. But see...here's the thing about that. Any guesthouse door on the first floor without a guest inside would necessarily not have a seal placed on it from the outside. After all, why would Erika waste duct tape? But...let's just assume that Erika completely sealed this door from the outside as well as the window from the inside and the outside, shall we? And we're left with an odd fact: Erika could not completely seal the doorway from both sides with her duct tape method if she had already sealed the windows from the outside.

Also, hate to point out a contradiction in Ryu07's red truth, but it's explicitly necessary for my alternative theory gaining acceptance: Therefore, during their entire meeting in the lounge, only Rosa went up to the second floor! This red truth flat-out denies anybody else could go up to the second floor during Erika's meeting with Nanjo and Gohda aside from Rosa, which is just silly if that's what it really means. That's because the whole rest of the red truth in the Court of Illusions would be meaningless to state if this red truth were truly a smoking gun, so I'm going to choose to believe that Rosa was the only visible party who went up to the second floor from Erika's POV (because that's the only rational thing one can conclude in this instance). Otherwise...yeah, it's only Natushi, so GG (and please...who really wants that unless you're explicitly for only Natsuhitrice?).

And about the marks on the seals...so what? What if Kyrie/Rosa stole some of Eva's duct tape and sealed that while discarding the marked seals? After all, we have the following red:

Eva's seal was of the same type as <Miss> Erika's. That is because this method of sealing was one that <Miss> Erika and Eva conceived of together after DINNER.

But we have this red which should make tearing the seals impossible, right?

Due to the above, the seals are guaranteed to be PERFECT. <Miss> Erika's seals were not broken by anyone, and deception is IMPOSSIBLE!!

Deception is impossible? Come now, Ryu07. Anything is possible. So...if I show how it is possible to bring deception on Erika by placing some of Eva's seals and discarding some of Erika's seals, do I get a gold star or something? And this is talking about Erika's seals, but how do we know Eva didn't help seal some windows/doors on the first floor of the guesthouse? The VN doesn't make this point clear. For all we know, during the break, maybe Eva gave Erika some of her duct tape. Actually...how does that even work? Whose duct tape was it originally? Eva's or Erika's? Things aren't making much sense here. When you try to nullify a possibility completely, that only makes someone want to come in and wreck it all the more, so you might as well not even bother trying.

Also, somebody did break Miss Erika's seals. I present Kumasawa, Gohda, and Nanjo as people who were outside of their rooms in the morning. But...oh my god...how is this actually possible unless Erika's seals got broken by someone?! *gasp* Did they...did they teleport OUT OF THEIR ROOMS?! Ye gods...Rokkenjima sure is a scary place, methinks...

Besides, if Ryu07 is truly open to all possibilities, he should have no problem in allowing for somebody to come and break these perfect seals. If anything, it shows that there are actually valid alternative solutions to his mystery, which he should be in favor of anyway. But...I'll proceed with my semantic arguing over definitions now.

All of Erika and Eva's seals were not tampered with in any way that hindered their ability to act as seals, such as being scraped off.

But Eva's seal had to be tampered with at some point by someone in order to find a dead Genji, right? Or did Erika and Eva just feel like leaving marks all over the damn place? And what if Shannon/Kanon wanted to scrape them off after the murders? It's their duty as servants, so could you honestly fault them for trying? Sigh.

And who said anything about tampering? Maybe Erika didn't place them well enough, and Kyrie thought they needed some adjustment because she was having an intense form of OCD? Is that meddling? Come on. We can argue about definitions all we want at the end of the day, but saying stuff is outright impossible just makes me want to break it all the more.

So, with that in mind, if I can show another party could come along to remove the duct tape seals on an empty first floor guesthouse door sealed from the outside as well as the duct tape seal on the window from the inside, then Kyrie can remove the duct tape seal from the outside and break the perfect closed guesthouse. Allow me to demonstrate the murder process now.

During the 1:00 AM break, Kyrie either has already handed off a letter with instructions to Rosa on what to do, or has made a phone call to George who is in the cousin's room. Rosa probably steals some of Eva's duct tape or takes some duct tape that Kyrie stole from Eva for this exact purpose.

Rosa is the only party who was seen by Erika in the lounge going up to the second floor. Oh, but did she actually go up to the second floor right away just because Erika saw her pass by the lounge? Well, not necessarily. Maybe she stayed on the first floor to remove some of Erika's seals on a guest house door before entering it. Hell, maybe she even removed Kumasawa's seal and got her to help.

But why would Rosa do this if it meant she was going to die? Well, Kyrie could have posed it to Rosa that Erika was working with Eva and she wanted to one-up them by showing somebody could get around their stupid seals. Rosa hates Eva, after all, so why wouldn't Rosa go along with it just to spite her older sister?

Or Kyrie makes a phone call to George and says she urgently needs to get into the guesthouse without Erika noticing for similar reasons. George is in the cousin's room, and the first floor guesthouse rooms are easily accessible to him without him even needing to appear in the lounge.

Therefore, Kyrie could easily get either Rosa or George to help remove the seals so she can bypass Erika's silly seals. It was impossible to reach the second floor guesthouse under Erika's seals? Psst. Please. Bern already said it was possible provided certain things worked out. And as long as you take off those seals and put new ones back on, Erika would be none the wiser. Besides, detectives like Erika and Dlanor have got no right to use the red truth the way the do in a fundamental sense anyway since they're not witches, so I don't mind playing dirty here by saying their reds about the seals are straight-up pointless conjecture meant to take away from actual mystery-solving.

Now, onto the fun part.
Pretty self-explanatory here. Kyrie and George/Rosa work together to remove all the seals, and George/Rosa unlocks the window for Kyrie. Kyrie then quickly heads up to the cousin's room and begins her murder rampage. Then she turns out the lights and heads back to the empty guesthouse room. She unseals Kumasawa's room to get her assistance in this matter. She leaves Kumasawa with two of Eva's seals (including the seal she helped remove for Kumasawa).

Next, Kyrie exits the guesthouse through the window and seals it from the outside. Kumasawa then heads to the inside of the window and seals it off with new duct tape (as well as locking it to preserve the illusion). Then, she seals the door back up from the outside (leaving it exactly as Erika left it) and heads back into her room which is still unsealed. And this is all possible for Kumasawa to still totally do with the following red truth:

In other words, after Kumasawa returned to the guesthouse, she never went to the second floor until morning. Nothing about that red prohibits first floor wandering, so I should still be good, I think.

Kyrie then hurries over to the mansion with a ladder to off Genji (whose windows are actually unsealed since Eva never went that far with her sealing unlike Erika). But...hell, Genji could have unlocked the freaking window for Kyrie and locked if after she slits his throat since he's basically an accomplice like Nanjo and Kumasawa are at this point. All he really had to do was make sure a ladder was present under the waiting room beforehand to help speed up Kyrie's murder run.

Then, after she's done, she scales down, disposes of the ladder (or she could have gone back and done it later in the morning), and heads back into the meeting following her short break. She could have done all this in probably about 15 minutes if she was really booking it, so that should have been more than enough time to constitute as a "short break" to everyone else.

But...oh wait, what about Kumasawa's seal? Well, did Erika even bother to check if Kumasawa's room was still sealed once she sealed Gohda in? Oh, wait...I don't think she did, did she? Welp. Guess she overlooked something pretty critical with her "perfect" seals.

So, simple problem for Kyrie to solve. While Erika is stalking Battler with her ears on the second floor after 3:00 AM, she casually enters the guesthouse to reseal Kumasawa back in her room so Erika is none the wiser.

This logic should account for all seals, because hey...Erika could not have feasibly sealed both sides of a door and both sides of a window all by herself (or even with Eva's help) without leaving somebody in that room, so my logic still holds.