The Gaki is a race of Japanese ghosts appearing in Buddhist preaches.
A gaki is described as a very thin, only-bone-and-skin man. Pretas are often depicted in Japanese art (particularly that from the Heian period) as emaciated human beings with bulging stomachs and inhumanly small mouths and throats. They are frequently shown licking up spilled water in temples or accompanied by demons representing their personal agony. Alternately, they may be shown as balls of smoke or fire.
When somebody died, he is reborn as another creature, in another world. There are six courses for rebirth below.
Those who reborn as a gaki in the world called gakido have dissipated foods in their lives.
In this desolated world, gakis suffer from endless hunger and thirst. They eat everything they can, even their children. This is the punishment for those who wasted precious foods.
It is said that a gaki wanders to this world sometimes. Though he would eat everything, he prefers human flesh and blood especially. Such a gaki is considered as a ghoul-like monster. Of course they are as intelligent as a normal man.
Since 657, some Japanese Buddhists have observed a special day in mid-August to remember the gaki. Through such offerings and remembrances (segaki), it is believed that the hungry ghosts may be released from their torment.