This study aimed to re-interpret the Chinese letters inscribed on the Suda Hachiman Shrine Mirror, which was controversial about the date and the origin of the production in the historical societies in Korea and Japan, and, on the basis of the new interpretation, intended to investigate the subject of the mirror production and the unique features of the inscriptions. As a result, it was confirmed that King Dongseong lived in the Osisaka Palace with the help of Younger Brother King (Emperor Yūryaku) while he was stayin in Japan, and Sama (King Muryeong of Baekje) sent 200 du of copper ingot to him. And it has also been elucidated that the mirror was made by King Dongseong after he returned to Baekje and ascended the throne with the bronze sent by Sama on August 10, 491, which was the 13th year of his reign. On the other hand, the inscriptions on the mirror allowed us to restore the uncertain royal genealogy of the Ungjin Baekje period: King Gaero and Gonji were brothers, and King Dongseong was the half-brother of King Muryeong. In addition, the genealogy leading to King Gaero, King Munju, and King Samgeun and the genealogy leading to Gonji, King Dongseong, and King Muryeong were confirmed.