If we're talking intense obsession in webtoons, I've been down a few rabbit holes lately. The one that still has a grip on me is 'Killing Stalking'. I know, super obvious pick, but it's the gold standard for a reason. That story lives in the obsession space—it's less about romance and more about a horrifying, co-dependent fixation that completely warps both characters. The emotional intensity is suffocating, and the art does a lot of the heavy lifting in making you feel that trapped, claustrophobic dread. It's not a healthy dynamic to romanticize, obviously, but as a character study of obsession, it's disturbingly effective.
Another one that comes to mind is 'The Beast Must Die'. It's a newer find for me. The premise revolves around a woman seeking revenge who gets entangled with a guy who becomes dangerously fixated on her. The art is gorgeous, which makes the unsettling moments hit even harder. The obsession here feels more calculated and manipulative, mixed with moments of genuine, twisted vulnerability from the yandere character. It’ school of thought where the obsession isn't just about possession, but about a warped desire to be the sole architect of someone else's world, for better or worse.