I've got a really vivid memory of finishing 'King's Game' because I remember being up at 3 AM, furious and a little confused. The whole manga is a relentless spiral, right? From the start, the king's orders just get more twisted.
So the ending... Nobuaki, our main guy, learns the king is actually the vengeful spirit of a girl bullied to death named Reiko. Her 'game' is her revenge on the entire class. In the final, brutal order, he's forced to fight his friend and last surviving classmate, Chiemi, to the death. Nobuaki wins, becoming the sole survivor, but he's completely broken.
The very last panels show him years later, living a hollow, haunted life. He's basically just waiting to die, believing he'll meet Reiko again. There's no victory, just absolute devastation. Honestly, it left me feeling kinda empty, which I guess was the point, but it also felt a bit nihilistic for nihilism's sake. I wanted something more, maybe a sliver of meaning in the carnage, but nope.