This article contains spoilers for Berserk chapter 369!
An ostensible source of the intense negative emotions besetting Guts after Casca's capture in Berserk finally positions the series' normally victimized woman in a place of power, as she deserves. Of course, readers only know what Guts could be feeling based on the few thoughts he musters, but the hope that everyone is likely holding onto is what Guts doesn't think or say.
When Berserk first introduced Casca, fans only knew her as a powerful woman who fought alongside her male counterparts and exceeded them and their foes. While mangaka Kentaro Miura did show her emotionally vulnerable through the ways in which Griffith obviously favored Guts over her, it was Casca's strength and resilience that inevitably stole Guts' heart and freed Casca from Griffith's hold. But all of that changed when Berserk transformed her into the ultimate victim whereby her assault at Griffith's hands broke her mind, putting her in a near catatonic state where she adopted the childish role of Elaine for years. Even when Casca became herself again (thankfully thanks to her two female colleagues and not Guts), just the mere act of seeing Griffith caused her to faint, allowing Griffith to capture her in recent chapters of Berserk.
Although once again making Casca a victim, how Guts reacts after Griffith flies away with her in chapter 369 by Studio Gaga restores the power she so desperately deserves. A wave of emotions overcomes Guts as he struggles with his sudden loss, including defeat, severe regret, sadness and fear. But all Guts thinks during this time is that he wasn't able to land a single blow on Griffith, nothing more. Berserk proves Guts isn't close to forgiving Griffith.
Throughout this whole ideal, Guts is shown displaying these differing emotions. Aside from that one aforementioned thought, the only sounds he makes can be attributed more to labored breathing than anything else. This is noteworthy because he could have thought or said a range of things. Yet, he's only driven to worry about the fact that he couldn't hurt Griffith. This likely proves that his number-one concern is how much more powerful Griffith is than him and how closing that gap likely seems more impossible than it ever did before even after everything he's recently gone through. He's basically right at square one after the Eclipse. This leaves room to assume that Guts could therefore be less concerned over the fact that he just lost Casca, and it's possible that the reason for this is that he believes she's more than capable of holding her own. Guts could have easily thought or said something about how he can no longer protect Casca or that Casca is now at Griffith's mercy. It would have been normal and understandable for him to express such sentiments. But it would have placed Casca once again in a position where she's portrayed as a damsel in distress who needs to be saved. But Guts' reaction proves that she's anything but that (and it's true). He's more concerned about his own failings and how much more powerful Griffith is than him.
Of course, Guts will still be driven to rescue Casca as is expected. It's an understandable reaction to such an unfortunate incident. But at least Studio Gaga gave Casca this moment of power after more than two decades of perpetual victimization. That said, while Casca's recent strength might come from her male protector and not herself, it's critical to note that a man who cares for her deeply and has devoted his entire life to restoring her is more concerned about his own failings even though she's the most vulnerable she's ever been since she was last captured in Berserk.