Japanese Halloween is a kind of Wakon-Yosai (和魂洋才), adopting a Western culture but in uniquely Japanese way. It's like breathing a Japanese life into a Western body, so to speak.
Before Halloween became popular in Japan, there was a such thing in Japan called Cosplay (コスプレ), or Costume Play, "an activity and performance art in which participants called cosplayers wear costumes and fashion accessories to represent a specific character". (Wikipedia)
Here is a sample of cosplay by the current Tokyo Governor, Yuriko Koike, for a Halloween party a few years ago:
https://www.sankei.com/photo/story/news/161029/sty1610290008-n1.html
Japanese Halloween is in fact nothing but a festival for cosplayers, without reference to stories behind Halloween, a peculiar Japanese practice in which its meaning is dropped and only its form is adopted.
You can see this practice, for example, in some Japanese weddings that are performed in Christian forms, but without any Christian faith.
Now, Japan has a long history of cosplay in traditional performing arts:
Kabuki - https://en.wikipedia.org/wiki/Kabuki
Kagura - https://en.wikipedia.org/wiki/Kagura
Noh - https://en.wikipedia.org/wiki/Noh
etc.
