He has Susak syndrome and she has hyperamnesia.
He was originally a proud man of heaven, talented and well-off family. Once you faint, you will only have one day of memory.
She has been tortured by super memory since she was a child. She has not benefited from it, but has suffered endlessly from it.
The gears of fate turned, causing him and her, who were originally two parallel lines, to meet at a point in time and space.