There isn't really an official 'Harry Potter' day. Fans probably read the books, watch the movies or do something related to the series.
No, such a day does not exist. Many Harry Potter fans consider the 2nd of May (the day of the final battle) to be Harry Potter day.
HARRY POTTER YOU DUMMY!!!!!
Harry potter and the chamber of secrets
Yes, Japanese people do know about Harry Potter.
The creatures in Harry Potter that drain people of their souls are called dementors.
The Non magical People in Harry potter bokks are referred as "Muggles".
Yes it's on march 22
You can find the answer on a website called Fanfiction. There are fic where people write about Harry Potter reading Harry Potter and The philosopher's stone and so on...
Harry Potter and the Deathly Hallows.A lot of people make the mistake of calling it Harry Potter and the Deathly Hollows.
Yes it it is celebrated it many countries in Europe and the Middle East.
Harry Potter and the Goblet of Fire
There is no last day...