Okay, so, I was confused on the trailer for a while and honestly a little put off at the whole "villain" vibes I got from it. But... I feel like there's something deeper going on here. Just hear me out:
"23rd Neural Control Experiment"
Pay close attention to the word, "Neural," to do with the brain and the nerves, as well as "control." Then, we see him struggling.
He's moaning and groaning, almost as if he's trying to fight against it. He looks like he's pain and then suddenly,
He's fine, he's IN control. His whole demeanour changes momentarily and all the lights around him come to life, it's not chaotic anymore. Until,
He wakes up, as if from a dream, absolutely terrified. He's sweating and scared, he's almost relieved to realise that it was a dream. But... What if it wasn't? I have always bought into the theory that Caleb and MC were brought together as a part of a bigger experiment by Ever, to test their evols and how they would get along.
Caleb has always been experimented on to better suit the needs and purposes that Ever plans to achieve with him and MC. He is being mind controlled by Ever, it's a "Neural Experiment" after all, Ever is trying to gain control of his thoughts and feelings, to make him detach himself from the MC to be able to use his telekenisis/gravity manipulation evol more effectively. Caleb seems unaware of this, he thinks that all of this is a dream when it's likely not. It's a result of all the poking and prodding Ever did in his brain since he's been a child. And Caleb's feelings for the MC are so strong that he's always able to fight against it, even if he is aware of it.
Ever blew up their house, likely because they thought that if MC knew that Caleb is definitely dead, they'd be able to keep her away from Caleb and keep Caleb away from her, making it easier for them to manipulate his brain to their liking.
Caleb is a sweet guy. The moment I saw him in the game, he was instantly the "protective-older-oppa-niichan" archetype. And this sudden shift in him in the trailer made me feel... Strange to say the least. It was absolutely jarring. I don't think he's evil, I think he's being made to think he is evil.
The still from the trailer below; it shows what is likely his apartment and everything is boxed up, it's almost as though this is from the day he moved to skyhaven or a few days after.
(side note: it's kinda cute that the only thing he unpacked is that photo of, what I assume is, him and the MC on the left.)
This is most definitely the past because,
He still has the necklace and he seems as soft as we know him to be, he caresses the necklace with care and in memory, almost as if he's consoling the MC like, "I'll never hurt you, don't worry." (And well, also just because he misses us and wishes she was with him.)
And then, this beautiful dream-like scene, almost from a memory changes into something far darker.
It's as though he's not himself anyone, he's someone who has been twisted. Ever has succeeded and it's up to us to make him remember again.
To add: the apple symbolism. His art and his motifs are often littered with apples and snakes, snakes are often seen as symbols of seduction, betrayal and most importantly: duality in most world mythologies and the apple, it's quite literally the seduction and fall of Eve/mankind. Even the snake, the devil takes the form of a snake when trying to seduce Eve to eat from the tree.
Perhaps the snakes at meant to represent his duality, and Ever as they are the reason for his duality in the first place. Meanwhile, the apples: his fall orchestrated by Ever. Ever is the devil and Caleb fell for their trap, unknowingly just as Eve did.