Ne-no-kuni, the stem word being”ne” meaning “root” (lit. World of Roots) – may possibly have the same root origin as the Proto-Indo-European equivalent word for “Netherworld”.
From Middle English nether, nethere, nithere, from Old English niþera (“lower, under, lowest”, adjective), from niþer, niþor (“below, beneath, down, downwards, lower, in an inferior position”, adv), from Proto-Germanic *niþer, *niþra (“down”)
From Proto-Indo-European *ni-, *nei– (“in, down”); akin to Old Saxon adjective nithiri (“nether”), adverb nithar (“down”), Old High German adjective nidari, nidaro (“nether”), adverb nidar (“down”) (see German nieder), Old Dutch nither (see Dutch neder) Old Norse adjective neðri, neðarri (“nether”), adverb niðr (“down”); all from a Germanic word that is a comparative of a word akin to Sanskrit नि (ni, “down”), Albanian nën (“under, in”).
In the Japanese conception, the phrase “Ne-no-kuni” conjures up a cavernous Under world that is below this one (Middle Earth), in the Realm of the tangled Roots of the Cosmic World Tree. See the entry in “The Encyclopedia of Shinto”:
Literally, “Land of the Roots,” it is also known as Nenokatasukuni, Sokonokuni, or Hahanokuni. It is the place to which Susanowo is banished by his father Izanagi, who says to him: “Thou mayest no longer dwell in this land.” From this we can deduce that Hahanokuni-Nenokatasukuni refers generally to any place other than Takamanohara (High Heavenly Plain) and Ashihara-no-nakatsukuni (Central Land of Reeds). It has also been speculated that it is another name for Yomotsukuni. According to the Engishiki [Procedures of the Engi Era] concerning the Great Purification (Ōharae) that takes place on the last day of the sixth month, Hayasasura-hime, the female deity who rules Nenokuni-Sokonokuni removes on that occasion all manner of sins, thereby effecting the cleansing of what is called the “sins of the four corners of the land below heaven,” that is, those of the entire country.
See also Yomi — Nishioka Kazuhiko