This is the future.
Technology has advanced to the point that it is now possible to edit human memories.
Light had always had a troubled relationship with his dad. His addiction to his cellphone and his fights with his girl had led him to ignore his dad.
His dad had brought him up by himself. He was always there, selflessly working away so Light could have the best future possible. But Light had never appreciated all this.
And now that his dad had passed away, Light wanted to make amends. In whatever way possible. Including editing away the bad memories and saving the good memories.
However, the technology still has some glitches and instead of saving the good and deleting the bad, attempts to do it the other way round.
Just when Light thinks he’s going to lose his most treasured memories, he’s in for a surprise.
It turns out technology can never beat human emotions.