Crazy obsession looks good on So Ji Sub as he plays a brooding, merciless thug in the new webtoon turned Netflix series Mercy For None. A violent K-drama that takes the action to a whole new level.

Adapting a hit webtoon into live action has become a go-to move for drama creators, lowering risk while guaranteeing a ready-made fanbase eager to leap from digital panels to episodic storytelling. It ...