In Tokyo, Japan, there was a Yakuza family. There are very famous amongst the Japan’s organized crime syndicates. Hamaa Genji, 87 years old, was the man who’s standing behind the Japan’s number one Yakuza, Kanto’s Sharp Fang Association.

The Young Master, 19 years old Matsuyama Yuki (Ham Eunjung) is his granddaughter and the only heir to take over the next Third Head Boss position when she’s turned to 21. At 6 she was called the ‘Chibi Waka’ (Little young master), and at 17 she inherited the Wakagashira name of the Kanto’s. The latest achievement, she went up against Chiba’s Toramaki Gang association, a group who was trying to spread their power into the Kanto District alone.

As she’s trying hard to spread their power and gain the trust from the gang to take over the position of Boss in another 2 years, her efforts completely turned to waste when her father come to Japan and want to take her back to Korea.

While in Korea, the person in charge to take care of Eunjung was Kim Jinsoo. He once worked as the guardians who had to protect the heir of famous and rich people. Due to the problem he had encountered during last mission, he had to quit his profession after he’d been warned by his own son, Nickhun, who work as International Police.

In order to hide the mission from Nickhun, Jinsoo decided to put Ham Eunjung under his own son care, one of Senior High School Students, 17 years old Kim Myungsoo.

What will happen when a yakuza meet with the high school student? Can he protect her from danger or vice versa? How Nickhun react when he know the truth about Eunjung?