Tamil and Japanese

It wasn’t Hindi but Tamil that I was thinking of. Both are Indian languages. Susumu Ono seems to be the prominent champion of the Tamil-Japanese theory. The following paper explains the relationship between the language from a linguistic perspective. THE GENEALOGY OF THE JAPANESE LANGUAGE -Tamil and Japanese - Susumu OHNO.However, a page about Ono on Wikipedia doubts this theory.

The Hypothesis on a genetic link with the Tamil LanguageOver the last three decades, Ōno has won particular notoriety for his support of the hypothesis, first put forward by Susumu Shiba in 1970, and developed by Akira Fujiwara (藤原明), most notably in 1981 [1] that the Japanese and the Tamil languages share a common ancestry. [2]. His theory has been severely criticized by the greatest living Japanese indologist, Tokunaga Muneo (徳永宗雄), [3] who, unlike Ōno, is fluent in Tamil, and by other comparativists like Kazama Kiyozō (風間喜代三)[4]. Generally speaking, this, like many other amateur hypotheses about the origins of the Japanese language, collapses because the author, though a top-ranking scholar of Japanese, is not familiar with the intricate complexities of the comparative methodologies of philology. Ōno’s attempt to confront his critics, in the article cited here, is successful in disarming Roy Andrew Miller’s critique, but fails to answer the general charge, made much earlier on his previous theories about an Austronesian origin for the language,[5]. The argument for a similar word order in Tamil and Japanese, for example, also holds for Japanese and some Papuan languages.      

I’m no linguist, and know nothing of Tamil, but it’s interesting to know that the origins of the Japanese language are still debated!