The Lord of the Abyss, Tartarus, was distraught over the death of Gaia and jumped into the Reincarnation Pool. In order to fulfill Gaia's wish, she activated [Twilight of the Gods] - the age of the gods is over... From today on, humans will be the masters of this world...
Tartarus was reincarnated into a lively girl named Carolia, who became the sister of the three giants of the underworld.
Carollia accidentally discovered that Athena was the one who harmed Gaia for the ownership of the earth, so the Millennium Holy War began.