In Japan people don’t go trick or treating like they do in the western countries that celebrate Halloween.Trick or treating means ringing the doorbell of the neighbours and this is considered rude/bothersome in Japan. A lot of the Japanese culture is built around not being bothersome to other people and respecting others.
But boy do they celebrate Halloween!
Cosplay/Costume play is rather big among the Japanese young adults. So for Halloween a lot of people dress up and go to parades and go clubbing in Japan. A good example are the crowds that gather in Shinjuku, Shibuya and Harajuku.
Large groups of friends tend to all dress up the same or similar. Though like at cosplay conventions some of the cosplay can get very elaborate.
Various of shopping malls, clubs, livehouses (concerthalls) hold events in the Halloween style. There are parades and shows.
Some of the parades or parties you can attend;
Shibuya fes is a large Halloween themed parade and flashmob, 20 and more bars and clubs are connected to it and Shibuya is parted in four different areas.
Halloween Pumpkin Parade in Harajuku Omotesando.
A lot of young families go to this parade, it starts from the Jingu Mae Elementary School and goes on for 1 km. This is family friendly but you do have to make a reservation to join in.
This was the very first place to celebrate Halloween in Tokyo. The entire park is decorated and you can buy limited edition souvenirs.
Naniwa Halloween in Osaka
This huge party in Osaka is first and foremost a comedy evening, multiple floors with each floor having its own party, djs and bands playing.
There are of course far more events in Japan. Especially in large cities!
You can check some of them here!