Yurei (Ghosts)

For reasons unknown to me, Shinto does not deal with death and funerals. In modern Japan, funerals and graveyards are handled by Buddhist temples. Nonetheless, Shinto asserts that all people are endowed with a spirit or a soul, called reikon, and when we die, we all become kami. Those who die peacefully and happily among their family members become revered ancestors. Ancestral spirits protect the family, it is believed, and every summer they are welcomed back to the family home during Japan's Obon festival. Those who die unhappily, or violently, or without a family to care for their departed spirit, or without the correct funeral and post-funeral rites, become hungry ghosts (one of the lowest states of existence in Buddhism. These hungry ghosts wander about causing trouble; they are typically called yurei (tormented ghosts). Most younger Japanese don't remember that the Obon holidays are also a time when the gates of hell are uncovered, and the hungry ghosts allowed to return to their ancestral haunts.

http://www.onmarkproductions.com/html/shinto-concepts.shtml#suijin