In the ordinary lives of Taehyun Choi and his sister Hakyung Choi, a revelation disrupts their world. Taehyun, struggling academically, stumbles upon the shocking truth that they are not blood-related. Just as he gears up to confront Hakyung, a tragic accident erases her memories. In the midst of this turmoil, their bond transcends mere siblinghood, evolving into something deeper and more pivotal.