I know it's not perfect, the early few tens of chapters are a bit of a slog, but it's incredible. You can see the author changing, getting older through the changes this webtoon went through. Slow burn into fireworks, into nukes going off in the sky kind of story you know? (It's also beautifully drawn) Note that the author went and learned mma, went around learned various other combat styles to prepare writing this story, but he enjoyed lifting and mma far more than drawing, hence the hiatus.