Cha Young Jin is the first female to ever work as a bodyguard in the Presidential resident, Chungwadae. Young Jin and Yoo Gwang Pil work as bodyguards assigned to watch over the president's son, Kang Soo Ho. They are assigned to guard Soo Ho for 15 months.

Young-Jin, a 27-old-lady with natural born pride and desire to succeed and be recognized is not backed up at all by her poor family; rather she needs to take care of all of messes and fusses that her grandfather, father, and younger brother committed. Having nothing to trust except for her own body and soul, she exerts herself to finally be appointed as a body gourd of the Blue House of Korea. At the Blue House, Young-Jin meets Kwanpil, a smart, excellent, cynical and charismatic colleague, who by instinct recognize each other as formidable rivals. They bump into each other at every course of training, extremely competing to beat the other, and what a mischievous fate! They end up being partner to protect Suho, the only son of Mr. President. Suho is an unstoppable rascal with high intelligence and violent nature. Suho is the key person who discloses the past of Kwanpil and realizes the true virtue of family and love. By describing two vivid characters Youn-Jin and Kwanpil, [Formidable Rivals] shows the life of body guards who by nature cannot be spotlighted. This is the story of the others, non-heros, who support protagonists. They also have their own way of life, own value of family and love.