[answered on: 2/7/2022]

There's enough ambiguity in the game itself about whether or not Basil or Sunny were the ones that killed Mari, and I believe that is very intentional. In fact, this is the crux of the divide between Basil and Sunny in the game, this is what is they are struggling to confront. I think the point of the "Something" -- that is, the visage of Mari's eyes open upon hanging -- is supposed to evoke doubt in us, just as it did for Basil and Sunny. You're supposed to think, oh, god, was she REALLY dead when they hung her body...?

This is the question that haunts Basil and Sunny into the present day start of the game. They DON'T KNOW for sure, and at this point, they CAN'T KNOW... and it eats away at both of them. On the day of the incident, they both realized that they don't actually know one another as much as they thought they did; by witnessing each other do things that really horrified one another. The ambiguity is a major part of why this circumstance is even more upsetting than it would've been without it (and make no mistake it would be miserable no matter what...) I think both Basil and Sunny alternate between self-loathing, and fear/resentment of the other, as a result of this. They just don't know how to feel about the other...!

For Basil, he is denying that Sunny hurt Mari at all, because he cannot reconcile this action with his idea of Sunny. Basil justifies that SOMETHING else had to have pushed Mari, and ruined his photo album, because he never would have thought Sunny capable of such things. And for Sunny, who was shut down and completely dissociating throughout this event, he... is terrified with what Basil did to Mari, by setting up this lie. It doesn't matter if it was to 'protect' him, because the fact that Basil could think of this and guide Sunny to assist in it ALONE is what is so scary, to Sunny.
But fwiw, I think Sunny is so far from broaching the thought of "Basil killed Mari" and instead is struggling to even accept the idea of "I am afraid of Basil", and this compartmentalization is represented through headspace Basil and Basil's Stranger. Headspace Basil is sweet voiced and encapsulates the Basil that Sunny knew in the past, while the Stranger represents the side of Basil that caught him completely off guard and looms about, yelling at him to not leave him and also deriding him about his actions. I even think the name "Stranger" is very apt, as it is as though Basil morphed into an entirely foreign, unknown individual in Sunny's head, and he just can't... merge this reality with the Basil he knew in the past. We really see Sunny struggling and oscillating between "Basil, the nice boy who loves flowers and photographs us" and "BASIL, SCARY, PERSON WHO HURT ME! WHO I CAN'T BE AROUND" ... *STABS IN MY BRAIN*... (I know that Basil being harmed in Black Space/by Omori is about Omori repressing the truth from Sunny, but, I can't. Not. Psychoanalyze Sunny on the method of this repression. Because it starkly contrasts how Omori feels about Mari -- who is arguably the root of the 'truth'. There's no need to ATTACK Mari however... Mari is not such an overt 'threat'. She is merely a guiding force trying to massage Sunny towards catharsis. It feels meaningful to me that Mari, even as Something, still only expresses that she loves Sunny, while Basil is used as a tool to heckle and deride...)

Anyways, I think by nature, being alone with headspace Basil ALWAYS is going to be fraught because Sunny CANNOT bear to reflect on Basil too hard for too long.

I bring this all up because I think this is an important aspect of this entire scenario: that Sunny... is... afraid of what Basil did!

So let's walk things back to the incident/Truth; let's say Sunny did kill Mari. This is possible, as you can examine Mari in a memory of truth, and it states that she is not breathing. (Though, I still don't think this is absolute proof necessarily, since I do not trust 12 yo distraught Sunny to be fully capable of checking Mari's breathing or pulse...) *coughs* but anyhow, we're saying that Mari was deceased from the fall and/or between being transported into her bed upstairs.

Even if this was true, I still think that what Basil did was unnecessary and traumatized the both of them in the end, more than if Sunny had simply been found crying by Mari's side as their parents came home. Accidents happen and I believe between Sunny's parents and the police, it could be understood that it was a moment of passion sort of deal. And from then on, Sunny would just have to cope with the regret and self-hate of having harmed someone he loved very much, just because a moment of losing control over himself.

Staging a suicide just was so, bad, for both Sunny and Basil's brains, and for everyone. Err I mean I UNDERSTAND that is the point of the plot of OMORI naturally, I get that... I understand Basil was just a 12 yo who perhaps could not grasp the weight of what he was doing, and acted on various assumptions/fears irrationally. But... like...! The point of the game also is that it is up to you how you feel about these two. Do you think they both are equally to blame? Are they both monsters? Or are they both two kids who made a mistake and should be forgiven? Or... do you empathize more with the plight of one, not the other...? That's up to you

And for me, where I land is, that 1. I do personally believe that Mari was alive still, and died by the hanging. This is how her death was able to be confirmed by police/forensics, with no further questioning. 2. and EVEN IF Sunny did kill Mari, I sympathize far more with him having blindly pushed her back because he was mad... This could happen to anyone! He just wasn't thinking. At that point it is just genuinely tragic circumstance; if this had happened anywhere else it could've ended fine. It's not Sunny's fault the human body is very easy to BONK-!! kill. IT'S VERY SAD AND SCARY!!

But er. I can't sympathize with what Basil did. I have a lot more problems with Basil having all the premeditation to worry about what will happen to the friend group when this truth is revealed... and to then, walk Sunny through bringing the body outside, tie a noose, set up the toychest, create this entire narrative... And for Basil to now rewrite Mari's existence and memory as a suicidal girl. The misery this brings upon soo many people who loved and knew her...! That now everyone must think that she was secretly suffering, and they were all too ignorant to see... And it also makes it true that, Mari wanted to die more than she wanted to be with everyone. THE WAY THIS ALTERS THE MEMORY OF MARI IS SO EGREGIOUS!!! I'd rather someone think I fell over and died than that I CHOSE to commit suicide-!!

Like you know I get it, we don't have to hold fictional characters up to a moral code the same way we do with real people. But like, in that case, Basil hasn't done enough to make me feel like his plight was worth it. Since, Sunny proceeds to become a shut-in and Basil cannot bring himself to doggedly try and keep contact... Seems like you just fucked up and everyone was miserable and there were no gains. Omg!!!! If only Basil's lie to "protect" Sunny was even anything Sunny could benefit from, in any way. But the friend group falls apart regardless... No one's bonds were strong enough to last through this tragedy.

Basil and Sunny were not able to become closer in any way because of this. They just became strangers to one another!

So *waves hands* you're going to likely hear me jokily state, point blank, that Basil killed Mari, but I don't dislike him JUST because of this... It's his choices vs. Sunny's that are the issue. If Mari was still alive after the fall, then Basil escalated a situation to the point of no return, and killed Sunny's very beloved sister. But on the flip side, if Sunny did kill Mari, then Basil's coverup still was overly harmful and unnecessary. Sunny did not want or ask for any of this. I think it was less "to protect Sunny" and more to protect Basil's happiness found in the friend group, because he was so troubled and lonely. It just feels far more self-preservational in nature than sacrificial, regardless of how Basil perceives his actions. I mean, he is later stating he will protect Sunny again while cornering him and gouging his eye out with gardening shears while Sunny is terrified and resisting... This, to me, encapsulates that Basil "protecting" Sunny is misguided and unwanted. It only harms him greatly!!!!!!

I hope this all illuminates my feelings sufficiently :p