Japanese Emperors are said to be direct descendants of the Sun-goddess Amaterasu. As far as I know, Amaterasu married the Moon-god, her brother, but later on, she left him. But they did not have any children. In that case, how did Amaterasu become the ancestor of the Japanese Emperors? From which offspring of the Sun-goddess did they descend from? Who did Amaterasu have this "ancestor of the Japanese Emperors" with?
Based on this really neat family tree of the Emperors of Japan, I count 84 generations between Amaterasu and the incumbent Emperor Akihito (whose reign began in 1990). As a descendant of the first Emperor Jimmu, Akihito traces himself quite directly back to the "kami [divinity] who shines in the sky." Jimmu was a great-great-great-grandson of Amaterasu, the descent going [four generations separating them] as follows:
Amaterasu-ōmikami ➜ Ame-no-Oshihomimi ➜ Ninigi-no-Mikoto ➜ Hikohohodemi-no-Mikoto ➜ Ugayafukiaezu-no-Mikoto ➜ Jimmu
According to the Encyclopedia of Shinto, Amaterasu and her brother the sea-god Susanowo-no-Mikoto once performed a divination pledge ritual called ukehi in order to produce offspring. The ritual required monozane, "seed," for which these two kami provided some personal items. Amaterasu wore five hundred jewels called the Yasaka which she gave up for the ukehi and, from these, five male kami were born. One of these five was Ame-no-Oshihomimi, whose son Ninigi-no-Mikoto was a great-grandfather of Emperor Jimmu.