Seeing Rem recognize Subaru's breakdowns in 'Arc 3' reaction fics always gets me in a way the main series didn't fully explore. The thing is, in the show we're locked inside Subaru's head with his shame spirals, but reaction fics pull the camera back. You get to watch, say, Beatrice or Crusch process his frantic, self-flagellating explanations in real time. They see the gaps he leaves out—the sheer number of loops he glosses over, the physical toll he never mentions. That external perspective amplifies his inner chaos because we're seeing how incomprehensible it looks to someone who doesn't hold the save point. A good one I read had Wilhelm slowly piecing together that Subaru's 'foresight' wasn't tactical genius but the muscle memory of watching him die to the White Whale a dozen times. That moment of horrified realization from Wilhelm did more to show Subaru's loneliness than any monologue.
Those fics also dig into the mundane aftermath most adaptations skip. The show gives us the dramatic deaths and resets, but fanfiction lingers on the interstitial trauma—Subaru unconsciously flinching from a hand on his shoulder because in another timeline that person killed him, or him developing a compulsive need to confirm everyone's location every hour. That's where the inner struggle becomes tactile. It's not just 'I have Return by Death'; it's the thousand tiny fractures in his social behavior that the other characters notice and misinterpret, which in turn isolates him further. The best ones don't even need to show a loop; they show the psychic debris left behind.