Classical flowery names
These names were invented after the introduction of Chinese into the language, and they show up in historical texts for prehistoric legendary dates and also in names of gods and Japanese emperors:
Ōyashima (大八洲) meaning the Great country of eight (or many) islands, Awaji, Iyo (later Shikoku), Oki, Tsukushi (later Kyūshū), Iki, Tsushima, Sado, and Yamato (later Honshū); note that Hokkaidō, Chishima, and Okinawa were not part of Japan in ancient times. The eight islands refers to the creation of the main eight islands of Japan by the gods Izanami and Izanagi in Japanese mythology as well as the fact that eight was a synonym for “many”.
Yashima (八島), “Eight (or Many) Islands”
Mizuho (瑞穂) refers to ears of grain, e.g. 瑞穂国 Mizuho-no-kuni “Country of Lush Ears (of Rice).” From Old Japanese midu > Japanese mizu (“water; lushness, freshness, juiciness”) + Old Japanese fo > Japanese ho (“ear (of grain, especially rice)”).
Shikishima (敷島) is written with Chinese characters that suggest a meaning “islands that one has spread/laid out,” but this name of Japan supposedly originates in the name of an area in Shiki District of Yamato Province in which some emperors of ancient Japan resided. Note that the word shima, though generally meaning only “island” in Japanese, also means “area, zone, territory” in many languages of the Ryūkyū Islands.
Akitsukuni (秋津国), Akitsushima (秋津島), Toyo-akitsushima (豊秋津島). According to the literal meanings of the Chinese characters used to transcribe these names of Japan, toyo means “abundant,” aki means “autumn,” tsu means “harbor,” shima means “island,” and kuni means “country, land.” In this context, -tsu may be interpreted to be a fossilized genitive case suffix, as in matsuge “eyelash” (< Japanese me “eye” + -tsu + Japanese ke “hair”) or tokitsukaze “a timely wind, a favorable wind” (< Japanese toki “time” + -tsu + Japanese kaze “wind”). However, akitu or akidu are also archaic or dialectal Japanese words for “dragonfly,” so “Akitsushima” may be interpreted to mean “Dragonfly Island.” Another possible interpretation would take akitsu- to be identical with the akitsu- of akitsukami or akitsumikami (“god incarnate, a manifest deity,” often used as an honorific epithet for the Emperor of Japan), perhaps with the sense of “the present land, the island(s) where we are at present.”
Toyoashihara no mizuho no kuni (豊葦原の瑞穂の国)、”Country of Lush Ears of Bountiful Reed Plain(s),” Ashihara no Nakatsukuni, “Central Land of Reed Plains,” “Country Amidst Reed Plain(s)” (葦原中国).