Err, asian is more accurate but there has been some depictions of what seem like a Yatagarasu is egyptian stuff...I'm pretty sure it had a proper name though.
Here I found this off the net, it might explain a bit more about the Yatagarasu's origins.
When Izanagi returned from the land of the dead, he washed his face. Amaterasu emerged from his left eye and the Moon God Tsukiyomi came from his right. She is also the sister of Susano-Wo, the Storm God, who appeared from his father's nose. She is the most prominent member of the Shinto Pantheon, and the Japanese royal family is descended from her. Her sacred bird is Yatagarasu, the eight-handed (footed) crow, which may be identified with Yangwu, the sun-crow of China.
Apparently, Yatagarasu is considered a god in most cases (the 3 legged thing varies from story to story) and so there aren't many Yatagarasus out there or anything, so when I said Utsuho ate a Yatagarasu that's wrong...Utsuho ate THE Yatagarasu to gain the power of the sun and thus now she can manipulate Nuclear Fusion.
From the game's data, Utsuho had become a Yatagarasu after 'eating' divine power that a god gave her one day. Apparently, the "three-legged" thing is fulfilled by her having one concrete shoe, one with magnetic power, and a 'control rod' for an arm. The reason why this works is because of Gensokyo's fuzzy "enough faith can make anything work" system, combined with their "Gensokyo is fantasy land, so something that only exists in dreams on the outside can exist for real inside" rule. Controllable nuclear fusion power is still just a dream out here, after all.
Could it be simply that at the time the power of a nuclear warhead was often said to be equivalent to the power of the sun, so nuclear fusion being the explosion of that power which is also said to be incredibly bright, would be why they said the Yatagarasu was a crow that emitted a light so bright that it was called the sun-crow. Well that is just my interpretation.