What is it about the Japanese youth that is so fascinated about rediscovering some profound love they might have formed while they were so immature they can't even properly remember anything about it? It's like the whole shounen romcom has two possible points of entry for a female love interest - she was the male lead's lover from when he was four years old that he completely forgot about (but she still holds a deep, unshakable love for him), or she falls from the sky (and probably also met him when he was four and is utterly devoted to him). Is it some hopeless expression of the dissatisfaction of the predictability of life? A desire for some sort of shortcut from a boring, unfulfilling existence to a life of fortune and intrigue just by doing an inventory of one's childhood?
It's amusing in its own way when you realize that the "struggle" in many of these comedies is the male lead deciding when to eat the delicious cake(s) served up to him on a silver platter.