I am more than happy to explain my theory! I hope it'll be a good read. I need to point out though that i am not a native speaker, so forgive my mistakes, and my fav character is Griffith and my least fav is Caska. I'm saying this bc some things i am going to say might lead you to think the exact opposite lol, so...
First of all, as things are now i think the only two character that can fit into the behelit bingo are Caska and Guts - yup, i've read theories abt other characters too... but if i have to be honest here, i really dont think that Serpico or any other rpg character has the 'input' to do such a thing. Why? Because we know that the Behelit opens at the character's peak of despair and heartbrokeness, and i honestly dont think that the rpg group is compact enough to trigger the behelit even if they lose a member or another tragedy of kin. We might reach that point given enough character-bonding chapters, but Skull Knight is around now and he usually brings bad omes, so we can safely assume that something is in the air already.
So, we stick with Guts and Caska.
Women first: why i dont think and dont like Casca as the behelit's owner?
As i said before, it opens when a character feels true despair; we can safely assume that, even if she is now bonding with her group, she'd been... not there for the biggest part of the journey: their deaths, even if we put Guts as the killer, wouldnt trigger her to that point - given the fact that she had always thought of Guts like a mad dog, and her broken self openly disliked him: we'd need lots of rebonding chapters to untie that knot. So, what we have for Casca's character?
1. Moonlight boy/her kid.
The latter is a BIG NO NO for me: even though i've liked the fact that Miura showed us that Caska is healed but not cured, i cannot stand for the second time the Eclipse as a focal plot point for Caska. Not again. She'd been out of the history because of it for twenty years (she is the wound Griffith left, said the Beast, and i FELT that throughout these 300 chapters), and if she becomes an apostole... id consider her out of the story again. Even if she decides to go after Griffith (unlikely, but i am covering up all the opt here), i wouldnt see it as CASKA going after Griffith. Shed be gone for good this time, at least for me.
Gods help me if Miura makes Apostole!Caska joining Griffith! It would be a tragedy for Guts (leading him to truly lose himself) but in all honestly this choice would be Sakura-tier stupid (Sakura from Naruto, dunno if you know smth about that manga but this character really had been mistreated by the author).
Her kid. Again, the hypothesis are: Guts kills the moonlight boy - its not really important how, if he wears the armor or bc he discovers in someway that Griffith is there too - or she sacrifices the kid herself; lets skip the 'Guts killer' topic because in that case Caska will not sacrifice the boy, but Guts or the rpg group to save her kid, and we fell hard in the 'with no reason her heart knows bc she is a mama' bs.
Fast forward to the second option: She has no reason to sacrifice the kid for now, since shed been out of the history as i said before and she had met him when she was broken. Except for the illogical, instictual bond they shared during their first met, she is not aware of who the boy is - when she cried touching Griffith at the Hills of Swords could have been either because she saw her beloved one again or because she magically felt the connection with his vessel; still, This is Berserk and not a shojo (i hope). I cannot find a reason for her to sacrifice the boy even if he fits into 'give us a part of yourself' trope (as we see in the dreamland) - what would be important enough for her to force that heartbrokening choice? As for now surely not Guts life or sanity, not the rpg group wellbeing... maybe killing Griffith once and for all, at least his mortal body?
Id say yes... if Griffith wasnt litterally the one she'd give the sacrifice to. I mean, it would feel like a scam: the sacrifice of the moonlight boy's body, and by extention Phemt's vessel, is not going to resolve anything. Why do i think this?
Lets take a step back: when Griffith came back, the first thing he did had been searching for Guts, to see if anything would shake his heart. Basically, he is saying to the audience that first thing first he had tested his only weakness, what could potentially lead to his demise (if not treated in time). He tells Guts that he 'is free'. Miura shows us that Griffith's heart came to life, instead: but apparently it is the Infant's feelings taking their tool on him.
Now follow me: if such a careful person checked first on what he thought was his possible weakness, and he found another 'pebble' that can potentially be troublesome... would that person being basically 'meh,whatevs' about it? If harming the moonlight boy means weakening Phemt/Griffith (or threathening him in any way), would he be so easygoing about it? And i am not referring to Guts' group stumbling upon the boy- they are not the only threat out there. Lets say that the Skull Knight finds and harms the boy. Lets say that the Masked Apostole finds the boy. Hell, lets say that a full moon showed during the Demon Empire assault and Ganishka found the boy! They dont even need to KNOW that the baby is Griffith: if the kiddo can be harmed, and Griffith knows he exists and knows when he is going to come out... then he should put him on a damn leash. Astral being or not.
What the manga shows is that Griffith is basically 'meh' about the boy, and unless Miura suddenly has forgotten how to write this must mean that he doesnt care what happens during the full moon, that it doesnt threat him in any way (maybe is just because even if this body is destroyed Phemt will only reicarnate again, but lets be honest: apparently one of his superpowers is becoming hotter with every reicarnation, and have you SEEN how sexy current NeoGriffith is!? Damn, if that body dies his next mortal vessel will lit up as a firework in the instant he'll hatch!)
Sure we can find a way to make it work, if this is the way the story must go on Miura's plan, but with the infos we have now we can say that Caska's only valuable option for a sacrifice is the moonlight boy, and if Griffith doesnt care about the whereabouts of the kiddo, then her sacrifice would be pointless (if she CAN do a sacrifice, being branded herself... ) And would lead to Caska becoming an apostole (or dying), and we've already talked about why i dont like that plot twist.
In the little space of the ask box i hadnt been able to explain myself, but let me be blunt about what i think: the Behelit belongs to Guts. One of the reasons i think this is the weakest one, based on assumptions on the story so far.
We've already seen the fullest of an eclipse.
With the Slug count at the start, later with Griffith; think about if for a minute: if we see a group of friend slaughtered by the monsters of the astral plane, or even if they survive, it would be a retelling of the birth of Phemt basically; if we see a person-solo sacrifice (for example the moonlight boy done by Caska), that will be a retelling of the Slug Count story - i'm not talking about the ways it can happen, they are countless. I am talking about the concept of it. The plot itself. A sonet is still a sonet regardless the topic: you can write about everything, still there are clear grammar rules you have to follow. Same for a behelit-driven sacrifice in this context.
No, i think we're done with sacrifices as plot twists.
This doesnt mean that the Behelit will not open.
Guts is a weird character, let me be blunt again: i'll try to not go into a true character study bc this post is already long enough, but briefly i want to point out something, first story-wise and then by Miura's own words.
When Guts was still with Gambino's group, we saw that he was desperately trying to be valued by his paternal figure; weirdly, despite the abuses he endures, he is even more focused on gain Gambino's approval. Sure, he reacts with rage, with anger when Donovan tells him that Gambino sold him off, or when Gambino threw back in his face the money he gained killing a general... still, that same night, we find him thinking about the way he can gain more money to give to Gambino. He is still a kid, and he doesnt know any better than what he has: the constant abuse and the rough life of a mercenary - every kid is a product of the context they lives n, after all, they dont have the resources (mental and physical) to drag themselves out of their birthplace. This attachment is understandable, even if in every other panel kiddo Guts is shown as older than his age (and a killer too).
When he grows up, he is litterally picked up as a stray puppy from Griffith and the leitmotiv sings again: we have another person that forces himself onto Guts choices and life, litterally winning him over after stabbing him and dislocating his shoulder, and in exchange we have Guts litterally blown away by Griffith's sole existence (the famous ' you're mine' panel). Basically, more you can hurt Guts, more the damn boy is going to love ya. But he gain something positive too: he acquires friends, the friendship/love with Caska, he comes to care for his comrades and subordinates - he litterally has a new perspective in life, the warmness of a more-or-less funcional large family. And even his initial 'abuser' Griffith is now the person that values him the most, that falls apart when he leaves. I am not trying to retell what happened during the golden age, i am trying to give a potrait of adult Guts: someone that now has a taste of positive feelings. He is no longer the kiddo that didn't know any better.
Because in the peak of 'love&acceptance', when he makes love with Caska, we have a very focal knot of Guts character. Do you remember? He litterally breaks down and see himself in Caska's face. He tries to strangle what he's seeing, and that is himself. He blames himself for what happened, He even defends Gambino 'virtue' when the poor girl makes an assumption on what happended to him!
This speaks yards on Guts. This is interiorized victim-blaming at its finest. To me, it looks like the hate Guts proves towards himself, for sins he litterally doesnt have but he think he has, is much bigger than the hate he can prove towards the person that hurts him. And this doesnt happens when Guts is in a bad mental state, in a Black Swordsman-like arc.
Add this to the fact that Miura itself said that the purpose of Caska was keeping Guts revenge-driven. The first time i've read that, i squeaked like a duck: really, after your best friend and idol sacrifices your ass to the literal devil, do you really need the rape of your babe to stay revenge driven?! Isnt the betrayal, the delusion, the pain of that enough to 'declare war'?
We have our answer. No, is not enough for Guts, in fact when he came to know that Griffith screw everything up and got locked into the prison, the first thing he thought was that he had driven everything upon Griffith - and i dont agree with that.
Is he responsible for Griffith's breakdown? Yep, mostly because he had to be deaf and blind to not aknowdledge that he meant more than something for a man that risked his life twice for him.
Is he responsible for what Griffith did? Nope - there IS a certain amount or responsability you can take for someone's actions, and Griffith's choice was not in this range: if he'd been killed on a battlefield bc he was not focused, would be a thing. Literal self-sabotage is another. A heartbroken person can do stupid things, but you're not their scapegoat and they cant get away with everything blaming their choices upon you. Sad that Guts doesnt think that.
So, we can assume that Guts wouldnt stay revenge driven for long by himself, that maybe he would end thinking that Griffith's choices were his fault - so Miura gave him the fuel to his rage: Casca's costant reminder of the wound Griffith left, and Phemt's shadow.
And when Griffith comes back again... Guts obv loses his urge to kill - and this cant be!He says. But what he does, from that moment on?
Think about it: till the Conviction Tower, Guts had actively tried to reach Phemt. He fears that he is fighting a lose battle, still he tries, it doesnt matter if theyre not even on the same plane of existence of how broken his body is, or how far he sink into darkness.
But after the Tower, they met three times. The tower itself, the Hill of Swords, and briefly before the damn boat arc.
Not once we see the same furious, 'nothing can stop me from kill this god' Guts.
In the Tower, he is basically stunned by Griffith (and he loses the urge to kill at his sight).
In the Hill, he actually listens to what Griffith is saying (like hes hoping to hear something in particular).
In the city, Zodd litterally tells him ' get lost kiddo, Master's coming' and he gets lost.
Is just me, or he is actively trying to avoid their showdown?
Is not that hard to reach Falconia: we see Rickert doing it. He even slaps Griffith - if such a young boy can do the task, what is stopping Guts from doing the same? Outcomes of that encounter aside, he ahould at least try to come closer to Griffith - instead the only way he tried is into almost raping Caska.
What is holding him back, and why? Why he let Rickert stopping him, why he listens to Zodd, why at the Tower he just stares durmfounded? A possible answer is that Caska is now his priority, and he is a much better mental state than the SwA and LCA, so he is no longer clinging desperately to the past. It can be, and i think the Skull Knight is in Elfhelm to break that flebile 'hope' Guts still has.
But why is he withdrawing from Griffith? This clashs with what Guts character had look like till now - revenge aside, any person would want a sort of closure. Again i am not talking about killing Griffith, if it's even possible right now... but just doing what Rickert has done: he wants tonreach Falconia, doing it is not hard, why not trying?
I think that Guts fears that encounter. And i am not referring to the possibility of his death - he's not scared of dying.
He is scared of not wanting to kill Griffith deep down his heart.
He says to Rickert that he cant go with him because he 'cant really hate Griffith', but which character hadn't been able to do a thing in front of ' that face, that smile, that voice'? Who is the character that still longes for him? Who is the character that is still burned by that light?
Eventually he will face the truth: he cannot kill Griffith not because of the power gap, but because Guts himself doesnt want it deep down. After all, the Godhand said that to us: the person you love the most, the person you hate the most... the life you cannot take with your own hands, you'll give it to us instead.
This is how he will fall into the deepest despair. That's how the Behelit will open, which i think is Skull Knight's bet: he is litterally waiting for the excuse-Caska to fall apart.
I think i've made my point.
I am sorry if this had been too long - and i am still missing the ' what i think will happend and why it will not lead to a sacrifice but a battle of wills' part lol, but maybe i'll add it later - i can only say that we have similar view of what we want for Caska.
Forgive my mistakes, and thank you for your patience with me lol. Even if we dont agree on our view, its nice to talk with not toxic people.
