This implies an accomplice most likely among servants because in the case suggested by Klash, some of the bodies are fakes, the fakes would have to be delivered to the island and (unless they arrived on the same boat) stored somewhere. This could have been done by Gohda who bought food supplies prior to family gathering (i think mentioned in VN) The Doctor would also have to be onboard because he gave estimate of time of death.

SPOILER!!!!!
In the final episode of the second arch of higurashi, through time of death one realise fishiness of one character.
END SPOILER!!!!

There is another moment. I don’t know if the anime made an accidental mistake -i don’t recall this in the VN – but when Hideyoshi and Eva enter the parlour, Eva asks about missing people being in Kinzo’s study. However she only could have heard Natsuhi give Kanon an order to search – she didn’t say for what – outside.

Both Eva and Hideyoshi claim to have been in their bedroom. Given that both Kanon and Genji didn’t speak to Eva they didn’t have time, Eva shouldn’t have known of missing people.

P.S. Come to think of it, the weight problem could be partly solved by the wheelbarrow that Kanon used in the first episode. Could it be foreshadowing of him being on of the culprits?

I haven’t played the game (well, I AM playing it, but as I’m writing this my last save game is on the beach- so no extra knowledge there.

Nice theory and all but I think you are really misunderstanding Natsuhi’s character which is why the anime is doing so badly. Carry on playing the game and you will hopefully see a new light to her

I think it’s: Natsuhi

We have several suspects, but Natsuhi fits the bill the most. She is a woman and could easily fool Maria into everything, like convincing Beatrice wants this to happen, or as you said, make her paraphrase things or in the weirdest case, change clothes and act like Beatrice.

She also obviously survived, and disappeared quite a few times suspiciously as you said.

She also is the one that seems the most detached from everyone. The ONLY one she seems to love/trust is her daughter (although their relationship is very very very poor) and the head of the family, Kinzo.

But there are also issues. Kyrie’s doubts etc. Why use Maria, and why such a complicated letter and way of working? And then the crucial part: MOTIVE. There is no crime without motive.

Well the answer to that is one thing: the motive.

She cares allot for the family, actually, that’s her number one goal. But nobody shares this except Kinzo (and he lost hope). Even her own husband doesn’t care much for her cause. She in despair, has constant head aches, and people act irrationally when in such state.
SPOILER FOR HIGURASHI KAI::::
think about the ‘criminal’ in Higurashi. He/she was also in a bad mental state.
/////SPOILERS END 8D

So, as shown in her brief conversation with him, she only seems to have full support in Kinzo. She greatly cares for him (thus the family). He is the head of the family after all. And what does Kinzo want? Beatrice! Whether she exists or not, whether he is mad or not, he wants to see her. Natsuhi thinks that the family is the most important thing in the whole universe, therefore will she do anything to help Kinzo. Whether SHE believes in Beatrice or not – she TRIES to make her appear. But how? THE EPITAPH. That’s the key (she thinks) to summoning beatrice/ OR/ that’s the way to make Kinzo believe that Beatrice will be summoned.

“At the first twilight, you shall lift up as sacrifice the six chosen by the key.”
Six people need to be offered, so she does this.
ALSO! When writing this long post, I scared myself, as I gained more and more evidence for this theory. When I quoted this I realized that the epitaph shows even MORE proof.

Natsuhi received the ‘key’! She was given the key to Kinzo’s room, and perhaps with that, the key to his heart (or so she believed). Maybe she was caring for Kinzo in such a long time, but THIS made her do all this, after all it is written in the epitaph she thought! It must be fate/magic/madness! So maybe unconsciously this is a hint towards her being the criminal, or the thing that made her go over the edge, but it certainly is some nice evidence supporting this case. I didn’t think of it as I started writing and stumbled upon it when casually reading over the epitaph ~ this happened several more times as you’ll see if you continue to read on.

Why use Maria? Well, obviously, she is incredibly easy to manipulate (in the VN it is shown even more, with her repeating everything what everyone else says). She seems to be the only person (other than Kinzo) who believes in Beatrice, which makes this even easier. Natsuhi wants to show the family that Beatrice is coming ==> so the way with lending the parasol and the letter would be the best one.

When Kinzo throws out his ring she could’ve found it, OR! Maria found it while searching for the rose and Natsuhi convinced/manipulated her in giving/using it to her in name of Beatrice. This of cource, if Beatrice doesn’t exist, if she does, then the theory changes slightly into Natsuhi cooperating with her, but see the final notes at the end of this for that.

Also > the blood on her door. I have really to little information to say anything about it, and I don’t want to be ‘making things up’ just to make this theory more credible. But it has something to do with Natsuhi/Krauss perhaps. Anyway it points towards Natsuhi in one way or another.

Now for another piece of evidence I scared myself with when writing this. I was looking at the HINTS for the death people of the first twilight, just to see whether anything can be explained with them and BOOM! Evidence!

‘… chosen by the key’ is written in the epitaph. She picked her victims, and knows that they are sacrifices for Beatrice (see notes for a possibility that she doesn’t believe/does believe)
Smashing their faces seems to be part of this or something, perhaps to show that they are just sacrifices and that this is not a personal murder. BUT! TWO of them have only half of their face smashed. It really freaked me out when I saw it: Krauss and Shannon! Didn’t Shannon make Natsuhi incredibly angry during the day? It was an enormous disgrace for Natsuhi (mainly towards Eva) after all is servant incompetence the fault of the host (=Natsuhi). And Krauss, it isn’t shown well in the Novel, but it the Novel she was very mad at him/distressed/in despair, for not telling her about the gold piece he had earlier.
So she DID have personal reasons to hurt them and to let everyone know that they are dead. WHY she did that to their faces I do not know for sure to be honest, but when you look at the two victims that stand out, they proof more and more that Natsuhi is the murderer.

Now most of you should say: But wait! Wouldn’t she kill EVA then? I was wondering about that for some time too… until when writing this I read the epitaph:
“At the second twilight, the surviving shall tear apart the two who are close.”
Two people who are close will need to be torn apart. As Natsuhi prepares the ritual she knows that she will need to do this. She has killed all of the other couples already, and only Eva and her husband remain. It was planned.

Also: for some reasons why she wants to tear their relationship apart==>
Natsuhi had great troubles with conceiving a child, and Eva was really making her miserable with hers. She wants to tear apart that family, because of personal grudge. And maybe she thinks that doing this will be the worst thing she can do to Eva.
I think that in episode 3/4, the second twilight, something will happen with the relationship between Eva and her husband.
And maybe will Natsuhi kill her in the third twilight right? She has enough time to murder, and torturing her in fear, taking her relationship away etc. is way more evil. And only Natsuhi seems the person to hate Eva’s guts that much.

NOTES:

Beatrice.

God she makes this analysis hard. I know that this VN will have supernatural elements to it, as the Ryukishi seems to like that. So does she exists, or doesn’t she? For sake of this analysis it doesn’t matter that much, but I think (this is outside of the theory) that she does. Just my intuition.
OR it’s Natsuhi acting her out you see.

Because Natsuhi could have more reasons to perform the Beatrice summoning ritual. You can think of plenty yourself; Gold, wish to revive something (the honour of the family) to please Kinzo, to meet the person that made the family awesome. Plenty. I figured that her emotions towards the family, THUS Kinzo, and her detachment from the rest (hey! Just like Kinzo!) made her do all of this.

Whether she acts it out for Kinzo, or believes it herself, or acts it out to take revenge xD, it doesn’t really matter. The main unknown is whether beatrice exists and whether Natsuhi knows this. Perhaps they cooperate. Perhaps Natsuhi is mind raping everyone. PERHAPS NATSUHI=BEATRICE!. I cannot tell at this point, but even without filling in that blank, I have allot of evidence pointing towards Natsuhi.