Seo Jin-woo has a special condition called hyperthymesia which allows him to remember almost every day in perfect detail. While his father, Seo Jae-hyuk on the other hand, developed an Alzheimer's disease, making him lose his memories. When Seo Jae-hyuk was wrongfully convicted of murder, Jin-woo vows to prove innocence of his father. Four years later, Jin-woo becomes a lawyer to put the real criminal behind bars but bribery, corruption, and betrayals would not give him an easy road to justice.
Lived with his father after his mother and brother died in a car accident when he was young. Using his superior memory, he was able to become the youngest lawyer in South Korea after dropping out of high school to prove the innocence of his father before he gets executed.
A lawyer with a hundred percent success rate but is infamous for fighting the case for the rich and powerful regardless of whether his clients are innocent or guilty. He is known to speak Korean with a very thick Gyeongsang accent. When he first met Jin-woo, he was reluctant to take on his father's case due to the high chances of losing however, Jin-woo reminded him of his younger self, which softened his heart and made him take on the case, which he eventually lost on purpose due to pressure from Il-Ho company. He was signed under Il-Ho legal team after the case, but still supports Jin-woo deep in his heart. It was revealed that the car accident his dad caused years ago was the same accident that Jin-woo's family got into.
Apart from Park Dong-ho, she is the only one to believe Seo Jin-woo's father innocence and unconditionally supports Jin-woo during tough times. She helped her parents deliver Papa John's pizza while she was a university student. 4 years later, she became a prosecutor in order to fight for Jin-woo's father and believes in the ways of honesty and truth but is always hindered by her superiors bribed by Il-Ho company.
The twisted and rich antagonist, Nam Gyu-man, is responsible for the crime for which Seo Jin-woo's father is wrongly accused of. He is described to be ruthless and brutal, even having a separate legal team from his company to handle his misbehaviour. However, he is seen to fear his father's wrath terribly.
Living in a bubble of an upper class, she is the sister of Nam Gyu-man and is also adored by her father. She is also Lee In-ah's classmate and colleague, and is quickly attracted towards Seo Jin-woo for his amazing skills.
Il-Ho company's section chief and Nam Gyu-man's right-hand man. He is obedient and loyal to Gyu-man and is often his punching bag. :However, he does not agree with Gyu-man's extreme ways of handling issues.
A prosecutor who is described as excellent at fabricating stories in trials. He handled the trial of Seo Jae-hyuk 4 years ago and has since moved up the ranks quickly, becoming Lee In-ah's section chief and misusing his power to cover the crimes of Il-Ho company. He is also the rival of Park Dong-ho.
Upon finding a clue that suggests Seo Jae-hyuk is not the culprit, he informs his attorney, Hong Moo-suk, not knowing that Moo-suk sides with Il-Ho. He was subsequently found dead and is presumed to have committed suicide because of his daughter's death.