Halloween is an autumnal festival held on Oct. 31st. Originally,  this festival was to celebrate the harvest of Agricultural products such as pumpkin, corn, rice etc. It was also believed that this is a   religious event  to expel the evil spirits.  We have seen many pumpkin display everywhere called Jack-o'-lantern. This custom came from the USA.  The pumpkin is maybe a symbol of  autumnal harvest and is carved as an evil face. During daytime , children and their mothers join parties to socialize. In the evening, many young adults mostly female, dress up as princess , dwarf, vampire, geisha(Japanese traditional female entertainer), celebrities and so on. Japanese Halloween festival is a kind of cosplay show and getting popular every year. I saw many young people wearing such costume on trains and streets on 30th and 31st. This gives  us festive mood and fun.
Sibuya station square in Tokyo 2014  Oct 31st:image from the internet