Tiangou

The tiangou is a legendary creature from China. The tiangou resembles a black dog or meteor, which is thought to eat the Sun or Moon during an eclipse.

Tiangou eating the Sun
As a good spirit, it has the appearance of a white-headed fox. It brings peace and tranquility, and gives protection from all sorts of troubles and robbers. It is referred to by astrologers as a constellation guardian of welfare. This constellation consists of seven stars. In ancient China it was called "Dog" (in the constellation Ship).

As a bad spirit, it is a black dog that eats the Moon. According to the legends, as an interpretation of a lunar eclipse, after Houyi shot down the 9 suns in the sky, he was awarded with a pill that is said to make someone immortal by Queen Mother of the west, Wangmu Niang Niang. Before he could eat it, his wife Chang Er ate it, hoping she could maintain her youth. Chang Er felt her body getting lighter and flew away. Seeing this, a black dog that Hou Yi was rearing went inside her room and licked the remains of the pill. He then chased after Chang Er, getting bigger and bigger. Chang Er, terrified, hid on the Moon. The black dog ate the Moon, along with Chang Er.

After knowing this, Wangmu Niang Niang captured the dog. She was surprised to see that the dog was actually Hou Yi's. She assigned him to guard the gates of heavens, becoming Tiangou. The Moon and Chang Er was spit back out, and Chang Er continued living on the Moon.

Battle with Zhang Xian
Zhang Xian is the enemy of the tiangou. It is said that he protects his children from the dog god with his bow and arrows. He is often depicted aiming at the sky, waiting for the beast to appear.

He is the god of birth and the protector of male children. Many sought for him to give them male offspring and to protect their living sons.

Meaning in Japan
The term tengu and the characters used to write it may be borrowed from the name of tiangou, though this is still to be confirmed. Despite the characters, both creatures are independent mythological creatures with no common ancestor or origin. A tengu is usually depicted as a bird or man with a long nose and other bird-like characteristics, while the tiangou is a dog.