This short manga story takes place in Pokemon, but in an alternate universe. Here, Ash and the gang are older and attend some type of prep school. There are no Pokemon in the story (sorry, couldn't quite figure out how to fit them into a school and in a romance story), but the story does contain some referral to Pokemon. (heh, heh, confusing, but you'll see if you read).
Definition of Halcyon:
The word halcyon ('hal-see-yen) comes from the ancient Greeks. It was identified with a legendary bird (actually, the bird was a kingfisher), though the word is usually used as an adjective meaning calm, peaceful, happy, and prosperous. This is basically why the manga was decided to be called The Halcyon Days.
You might find the term halcyon days in relation to the sea. Well, it was believed to be a two-week period of nice, calm weather sometime before and after the shortest day of the year. There is probably a reason why this period was called halcyon days, but I don't want to get too carried away. ^_^ There will be some extra explaination for this in the story from Ancient Greek Myths...
There is a reason for this title, but you just have to read and find out! ^_~