Lu Yuan, who possesses inherited extraordinary skills, descends from the mountains intending to end the childhood marriage engagement arranged between him and Lin Yuhan. Along the way, he encounters Lin Yuhan in danger and steps in to save her. Due to a special restriction in the Lin family's ancestral Medicine King Codex, the two must maintain their engagement for one hundred days. Lu Yuan takes the opportunity to become Lin Yuhan's personal bodyguard, protecting both her and the Lin Group. When the company's new drug development faces technical obstacles and internal management challenges, Lu Yuan draws on his mastery of traditional medicine to refine the drug formula, overcome technical bottlenecks, and strengthen the foundations of the Lin Group's business. Over the course of their hundred days together, the two also begin a special romantic connection.