Why I think Morgan the Castle has BPD
This one is going be a lot shorter since we see Morgan much less than we do Ryan, but I still believe she can be read to have BPD as well! Very sorry if this comes off harshly worded!
✪ Morgan is shown to be incredibly hostile from the minute she has her physical debut in Infinity Train
After Kez arrives in the castle with Ryan and Min-Gi, we see that for however long Kez was gone Morganwas still incredibly upset by what happened with Jeremy. When Kez suggests that the two guys stay in the castle so that Morgan wouldn't be lonely anymore, the implicaton that these two... complete strangers could EVER replace what she had with Jeremy causes Morgan to fly into a rage. The assault escalates to the point of nearly suffocating the boys to death until Kez intervenes.
✪ Jeremy is Morgan's favorite person
When Jeremy gets his exit, Morgan is very devastated and continues to show this when Kez returns with two new strangers. According to Morgan, Jeremy took care of her in ways most passengers and even Kez usually didn't. Most passengers essentially used her (because that is the point as a denizen) only to leave her when they were done with her. This happening repeatedly over time began to take a toll on her. So when Kez accidentally helps Jeremy get her exit its just this massive betrayal from her POV and it sets her off and causes her to lash out at Kez (and Ryan and Min-Gi when they arrive).
✪ Morgan displays self-destructive tendencies
Morgan was very much willing to destroy herself (or the castle) if it meant harming Ryan and Min-Gi because their presence felt like a slap in the face to her after what happened with Jeremy. Self destructive behaviors. are common in people w/bpd
✪ Morgan splits
Splitting occures when a person is only able to see things in an absolute good or absolutely bad or evil. We can see this in the way she treats and talks about Jeremy versus how she talks to and treats our main trio. Jeremy is her saving grace, the only person who treated her as more than a tool to fufuil their purpose in the car. But to her, Kez is a monster for taking that away from her. Kez ruined her, took the only thing that made her existence worthwhile. And Ryan and Min-Gi are just collateral damage to her rampage. Just pathetic excuses of a posible replacement for Jeremy. They couldn't possibly be anything like Jeremy, let alone attempt to replace him. I could argue that that Morgan divorced the good aspects she loved about Jeremy (how he took care of her and kept her company) from the bad aspects that were the reason he was on the train to begin with (his looming guilt over losing his mother and sister in a car accident and being the sole survivor). As far as Morgan is concerned, the only version of Jeremy that exists to her is the one she grieved when he left, and not the one he was when he first arrived.