I really dig Schierke and Guts. They are my most favorite duo in any work of fiction.
They are both rather introverted and thoughtful personalities capable of change and learning. The interaction between them seems very harmonious and trusting. I absolutely love reading about them evolving to such a wonderful and caring friendship.
It’s no secret that Schierke is having a huge crush on Guts, for understandable reasons, considering she lacked a fatherly figure her entire life (then again who doesn’t have a crush on Guts in one way or the other?)
However, one interesting question is: How does Guts feel about Schierke?
From the beginning, Guts has been protective of her. Entering Flora’s Mansion, remember how Isidro teased her for touching Schierke in inappropriate spaces when they first met in volume 24? Guts gave him a knock on the head for that, telling him to leave the girl alone.
When Schierke was down or doubting herself, Guts repeatedly cheered her up and motivated her, e.g. during Enoch village or the Beach Scene. Because he is very observant and responsive, he knows what’s going on with the little girl:
At Enoch Village, Schierke is frustrated with the villagers: she received a rather rough welcome being a witch, and their recklessness regarding the resident water spirit upset her, too. [205-206] She thinks they are all mistaken in their ways. Because of this, her frustration shows through when she summons the resident water spirit once the Trolls invaded the village. [213-214] She is bathing herself in its power and the village is being flooded excessively as a result. She is blaming herself in the aftermath, even though arguably, it could have been the spirit itself going rampant because it hadn’t been worshiped for a long time, being starved of attention. Then Guts comes into play, who notices her tenseness, reassuring her that despite of being rough she still did her job well. After that, almost immediately she manages to find out where Casca and Farnese are via Od tracking.
During the Beach Scene,  again Schierke is lost in thought and sad because of Flora’s death. We see how Schierke mind-absently watches the ocean and loses her hat in the breeze. After Guts picked it up for her, she asks him whether he’s alright.  As it shall turn out, Guts noticed what’s wrong with little girl and brings it up when they talk below the moonlight: “You’re tryin’ too hard you know? You only distract yourself like that, so cleverly set in your own ways, worry about everyone but yourself [Emphasis by me].“
From what I’ve seen, Schierke is the only one who gets any physical affection from Guts, mostly shown as him placing his palm on her shoulder or head.
 Moreover, he described her as impressive sorceress, a reliable magic user, his lucky charm. Whenever I read him saying this, it feels like he is saying this full of pride, respect and admiration.  Similarly, after the Kundalini was slain in volume 31, Guts’ facial expression is so precious when he proudly tells Serpico how great of a combo he and Schierke were.
Guts opens up quite so when he is with her.  During volume 33 after Guts attempted to save Casca who jumped overboard, Schierke is about to redraw the amulet on his back. There, Guts states that even if you try to piece something broken back together it won’t be back to normal again, referring to his mechanical arm and metaphorically, also his (in)ability to save Casca alone. Despite of him being hurt as he says that, he doesn’t mind sharing that with Schierke. But it’s not only that: he doesn’t have a problem to be hurt and have her witness him being vulnerable. Here’s your reminder that the last person to see Guts vulnerable was Casca, which is an interesting and perhaps also provoking parallel. Guts voices gratefulness for the times Schierke has been helping him. He puts his trust and life onto her, counting on her that she will bring him back. Just ponder about this for a second. A guy like Guts, who’s been betrayed all his life, is giving so much trust into a little girl like her.
He knows the little girl is his salvation. He treats Schierke with deep respect and care, trust and gratefulness. He looks up to her, marvels at the little girl’s magical powers and is proud of their joint achievements. Her word has a lot of weight for him, because he knows she cares for him. I’m very sure Guts likes her quite a lot in return, even though he is not showing it directly.
What’s pretty cute about it is that Schierke feels the same way about him — and actually a bit more than that, given her crush.