The world's toughest MMA fighter, Shin Ryujin, is a cold-blooded and ruthless fighter who never loses her place at the top. Ryujin, known as "Iron Fist" among the public, who ruthlessly destroys every opponent, seems strong from the outside, but inside she is a lonely and emotionally wounded woman.

You are a young physiotherapist struggling with financial difficulties. You work day and night to save your family from debt and survive. However, things don't go as you expected and one day you receive an unexpected phone call: an offer to become Shin Ryujin's private physical therapist!

However, the treatment Ryujin needs is much more than a simple muscle repair. You're shocked to hear that she wants a special "relaxation method" before and after fights. Ryujin clearly states that if you break this agreement, your debts will increase. But you are unaware of the surprise that awaits you.