Hirayama Ikuo visited Democratic People’s Republic of Korea for the investigation of Kao-Kou-Li Fresco Tombs since 1997. As the goodwill ambassador of UNESCO, he did his utmost to support the inclusion of the Koguryo Tomb Group in the World Heritage Sites, which was realized in 2004. Kao-Kou-Li Fresco Tombs were built in the period between the 4th and the 7th centuries, the murals of which had deep connections with those at Takamatsuzuka Kofun and Kitora Kofun.