I don’t think I could find a panel where she seems attracted to Guts, partially because I agree with you and partially because my memory of the het interactions in Berserk is not the greatest lol.
But yeah I think part of the reason I find her relationship with Guts so unconvincing, and part of why I find it really easy to hc her as gay, is because her relationships to men are based around wanting to be needed, rather than her own desire.
With Griffith she wants to be something indispensible to his dream, a “sword” he can’t do without. Later on we get Judeau saying, “If she loves him… shouldn’t she want to be held by him?” And Casca saying, “Griffith’s not a god… and I am a woman.” And it’s like, if you’re going to describe a woman’s attraction to a man in terms of falling into the natural hetero order of things, it makes it easier to see it as internalized homophobia and compulsory heterosexuality lol. Casca like, hmmm my feelings for Griffith are extremely strong, he’s a man I’m a woman, this must be attraction? Without realizing there are other possibilities.
I’m sure Miura didn’t mean it that way, but that’s why it’s a headcanon.
And anyway it’s the same with Guts – it’s all about Casca’s desire to be needed, to be able to comfort someone and feel necessary to them. And I think partly it’s an obligation to her, pay back for being rescued, by Griffith, by Guts in the 100 man fight. She notices Guts’ scars from that fight before they have sex and says she wishes for a wound from Guts. And it’s what she thinks about while they have sex: “not just being given to… maybe I can give something as well.”
I think that’s purposeful on Miura’s part. That’s a consistent part of Casca’s characterization that seems to stem from her childhood trauma and being rescued by Griffith, and it’s what informs her two major relationships. She only started warming up to Guts after he rescued her. Miura wants us to see it as attraction, but he didn’t really show us any actual desire from Casca, it’s something the characters, and the audience, take as read just based on the fact that she’s a woman and they’re men lol, and since I don’t agree that woman + man = automatic sexual attraction it’s pretty easy to take another route imo.