The fundamentals of Japanese religion are at their ancestral worship.
Even after the adaptation of Buddhism, Japanese keep their traditional thinking. There is a distinction between this world of mankind and the other world for supernatural existences.
Man dies, pass the border to another world (in Buddhist thinking after 49 days from their physical death.)
Every summer, generally between August 13 to 15, people celebrate the Bon period. It is believed that ancestral souls come back to their home at the evening of August 13, and go back to the other world at the daybreak of August 15. Today is August 20th. In north Japan where there take a long Bon period (from August 6-20), this is the day we take back our normal daily life.
People dance through the night because, they say, there are not enough beds for all existences (mankind and ancestral souls). During the Bon period, all family membres gather together (at the country side, it can be even over fifty!), they eat and drink a lot, chat, dance, sing, etc. etc. until they fell in sleep by fatigue.
Materials are not all contents of the world. Once you believe in invisibility, it becomes the source of our vital energy. When people act as if ancestral souls are with them, people really live the moment with them. They spend time as the past when their dead family was alive.
Appart from our academic/scientific way of thinking, it is quite natural for human beings to want to believe the connection between their dead be-loved people. Not only in Japan, the ancestral worship is very frequent to another parts of the world. The death means, for them, only the end of one's physical life. Their soul still remains in this world (or in the other world). The death is not farewell but just temporally separation until the moment where you will see them again (even it looks too long for the person in sallow).
Conveniently, Buddhism is in Japan. People reborn again and again. It means in deed, the death is totally not farewell but just a break for one's soul.
For the first Bon festival of my young be-loved cousin.