Okay so trying to decipher this...
It seems the eldest sister in Korea, suddenly had a heart attack and went into a coma. Some time while she was in the coma, her younger sister died in a car accident, and when she woke up and heard the news she was relieved because she probably hate her younger sister for something not mentioned yet, either her beauty or kindness.
Two years later after waking up from the coma, she learned the "Truth" about her younger sister's death, implying that her younger sister either killed herself in a car accident to give her heart to her older sister who was in a coma for surgery or something to that degree happened. Older sister feels guilty about the fact she had previously celebrated her sister's death.
While wanting some time alone, she happened upon a kid who reminded/looked like her younger sister and ends up saving them from a car accident dying in the process and then is reincarnated into a world that supposedly her younger sister was also reincarnated to, by a "God" who seems to be directly involved/ingrained in the world over having a Laissez-faire policy.