We get descriptions about how Yuuya is feeling and what he is thinking that we do not receive about Game-Prefect, but this does not technically prove that the Game-Prefect was not experiencing those same thoughts and/or emotions:
When Grim declares he will be fighting Yuuya for his spot at NRC, for example, Yuuya is described as being “nearly in tears,” and while there is nothing in the game that insinuates Game-Prefect was also close to crying there is also nothing that disproves it, so in instances like this things could go either way: Yuuya-adjacent or otherwise.
Both Game-Prefect and Yuuya reflect on feeling sorry for Grim.
Game-Prefect has the option of two different lines disparaging Ramshackle Dorm when they first see it, neither of which are things that Yuuya says.
It is a significant moment in the game when Game-Prefect appeals to Crowley to allow Grim to stay with them, surprising Grim, and there is even a follow-up of additional beseeching from Game-Prefect when Crowley seems reluctant.
This situation was flipped in the novel, with Crowley unilaterally assigning Yuuya to Grim and Yuuya actually trying to protest against it.
When Crowley declares that Yuuya is to be a janitor at the school Yuuya starts to cry (“in his great relief, the tears he’d held back earlier rolled down his cheeks”), with an added description of how he is so grateful for the food, shelter and purpose he is being offered that he wants to hug Crowley.
In contrast, Game-Prefect has the option to respond “Fair enough” or “What choice do I have?”
When Ace tells Yuuya that he and Grim should be able to do the hundred-window punishment alone as the school’s janitors Yuuya is described as mumbling, “But, um, we were told to finish up before supper,” while Game-Prefect’s options are “There’s no “banging out” a hundred windows!” and “Headmage’s orders. You heard the man.”
The moment where Game-Prefect yells at the bickering Deuce, Grim and Ace is the same in the novel, down to how he scares Grim (in the novel Deuce and Ace immediately return to bickering).
The moment where Yuuya suggests they work together is also the same in the game, though novel-Ace’s dismissal of the idea is a little harsher.
Yuuya does not have any dialogue about the group becoming closer, while Game-Prefect has options to comment on how they have all come together.
Yuuya does not refer to them as friends (as of the end of the first novel he is still questioning if such a thing wouldn’t make Ace and Deuce mad at him, but neither does Game-Prefect: the line “We’re all really good friends” was added to EN).
Game-Prefect and Yuuya’s responses to being named beast-tamer and a student are nearly identical.
While Yuuya thanks Ace and Deuce for their help in the prologue’s final scene, Game Prefect does not.
Twisted Wonderland Reference Note 