The Hidarugami, also known as The Hunger Gods, are spirits of people who starved to death in the mountains. And because they died alone there's no marker for their grave and no ceremony, so their spirits become evil and seek to take revenge on hikers.
They are found almost exclusively on mountain trails and passes. Hikers and travelers in the presence of the Hidarugami are suddenly overcome with acute hunger, fatigue, and numbness of the limbs. The feeling is said to be that of actual starvation. The victim is unable to move and often collapse. This attack is a form of possession. The Hidarugami enters your body. If no action is taken, the Hidarugami can cause death—actual death by starvation in a healthy body.
If you are killed, you join the Hidarugami group, so that the group slowly enlarge to contain many souls. However, expelling the Hidarugami is easy. Just a small mouthful of a staple food, such as rice or grain, staves off the attack and the starvation leaves as quickly as it arose. That is why —even today— hikers are advised against going into the mountains without a few riceballs or a bento to eat and never eat their entire meal, always leaving a few grains behind in case of emergency.
Hidarugami defy simple classification, and show the complicated nature of Japanese folklore. Are they yurei (Evil Spirit)? Are they yokai (Supernatural Monsters)? Are they Gods? The answer is yes to all three questions.
Higarugami are most definitely yurei or onryo (Vengeful Spirits). But they are not typical yurei because they act as a group and actively make new members, and since they are bound to their location, they would also be considered a type of jibakurei (Earth-bound Spirit).
Hidarugami are also muenbotoke. This refers to the unworshiped dead, those who die without burial or ceremony. Special rites are often held on Obon, the Festival of the Dead to try and get their spirits to pass one. One passage says that the Hidarugami’s grip on the world is not particularly strong—that they are a weak god—and they should be banished by a simple muenbotoke ceremony.
-Ashkenazi, M., 2003. Handbook of Japanese mythology. ABC-CLIO.