I feel like the reason why Casca screams seeing Guts in chapter 359 is similar, yet different from chapter 355, covered in this article. There, it was somehow somewhere connected to Griffith and completely losing her dream of being something invaluable Griffith (she states so during the waterfall scene in the Golden Age). In chapter 359 however… it becomes clear to us why she really is having this kind of reaction on seeing Guts.
Let’s take a look at what happens in volume 23 first.
This volume is where Guts harms Casca: first he chokes her under influence of evil spirits, then sexually assaults her while being to his senses – however, let it also be mentioned he did break under the pressure and frustration he was facing due to the unrequited feelings he has for her, and she was also attacking him, to which he pinned her down as reaction. There are other important things happening in this volume that seems to connect to episode 359, but these are worthy their own article.
Either way – the imagery used in volume 23 and episode 359 is familiar.
As Guts chokes her, her scream snaps him out of it, causing him to resist the evil spirits and tell them to stop. As Casca lays unconscious, Guts then attempts to wake her up. Once she wakes up and sees his face, she lets out a scream of terror. This is us witnessing her forming a trigger: namely Guts’ face. Possibly also why she couldn’t remember his face in the passage of dreams (at least, surrounding the events from Conviction and onward).
Note Casca’s utterly terrified expression. After this, Casca runs away from Guts, until Guts decides to tie her up for the sake of her own safety.
Now in Episode 359, something similar happens.
Casca is having a flashback, first holding her stomach, and as Guts calls the first syllable of her name, she starts twitching and drops on the ground. As Guts instinctively turns around to help her because he is so concerned, Casca sees him and screams.
Casca’s expression is filled with fear, just like in volume 23. The reason why Guts’ face looks so absolutely devastated in this page is also because he is reminded of harming Casca the way he did back then: His face expresses both deep regret and anguish.
If Guts desires to be back close to Casca, he NEEDS to both show and tell her he does not wish to harm her (and also keep on doing it, so she can relearn he is no threat to her) – and Casca needs to let go of any negative feelings and thinking patterns she (sub-)consciously associates with him.
It seems like the next thing that will be dug out on Casca’s way to recovery is finding a resolve in Guts’ assault of her. That being said, Farnese and Schierke will have to be involved in this, too, in order to find resolve for it in the first place. I highly doubt Guts is going to be able to do this by himself.
Given how much Guts has change for the better I think it’s not going to be a problem for him – IF he decides to pursue this goal and overcome the pain that he is going to be exposed with doing so.