I think the quintessential example has to be the 'Komi Can't Communicate' fan-made side arcs that circulated on Archive of Our Own last year. They're not canon, obviously, but some of those writers nail the terrifying shift from her usual, painfully shy exterior to a possessive, obsessive interior so well. One I remember, 'Silent Echoes', had her slowly isolating Tadano from his friends by 'accidentally' misplacing his phone and subtly manipulating social situations, all while maintaining that angelic, quiet smile everyone knows. The horror isn't in shouting or violence; it's in the contrast between her actions and her utterly unchanged, serene face in public. It’s that gap—the immense disconnect—that makes a yandere Komi so compelling. The canon series gives us glimpses of a darker, more competitive side during the school festival or with other girls, which fanworks just crank up to eleven.
Honestly, I prefer the stories that keep it psychological. When she goes full-blown violent, it feels like it breaks character. The best explorations are the ones where her communication disorder twists into this warped form of 'love'—she can't express it normally, so it curdles into something terrifyingly intense and silent. There's a webcomic parody I saw once where she collects things Tadano touched in a little box, labeled in her neat handwriting, and that single image stuck with me more than any gory scene.