The Japanese myth of the dragon Yamata no Orochi being slain by Susa no Wo has many points in common with very similar stories about Indra slaying Vritra.
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In \_Slaying the dragon across Eurasia\_, Michael Witzel of Harvard wrote about the similarity of Japanese and Indo-European myths, among others. He considered explaining this by proposing that the ancestors of the Japanese met Indo-European people in Asia long ago. No direct evidence of this exists, but there is no reason to reject it either. He did not follow up on the possibilities created by this theory.
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One part he did not consider was the etymology of orochi. In Old Japanese, woroti ‘big snake’ is very similar to Avestan vërëthra- from \*wërëtra-, obviously the same name and myth as Vritra. If he believed the myth came from an Indo-European source, it seems this kind of match would be more than a coincidence. It seems best to gather all possibilities to see if the sum of the similarities makes mere chance an impossibility. This is just one of the many words showing the similarity of Japanese and Indo-European loanwords or cognates. Previous scholars have considered some of them to be related, and even the similarity of the word for ‘honey’ in Japanese and Chinese to \*medhu has been seen as evidence of the Indo-European Tocharians in the Far East spreading their language thousands of years in the past. Not all claims have received full agreement.
