In the Iksan area, archaeological ruins such as the royal palace, Mireuksa Temple, Jeseoksa Temple, Ssangneung Royal Tombs, and fortress walls, which are components of the ancient city wall, remain in better condition than those in the Gongju and Buyeo areas. In addition, there are documentary records that support the fact that the capital was relocated in the late Baekje period, proving that Iksan was also the royal capital of Baekje. However, because the direct record of the relocation of Iksan is omitted in 『Samguk Sagi』, many theories, such as “the transfer of the capital,” “another capital,” and etc., are being raised about the historical nature of Iksan in the late Baekje period. As part of the work to supplement the theory of the transfer of capital to Iksan during the reign of King Mu of Baekje, I seek to access the reality of King Mu (Seodong) and Princess Seonhwa who appear in the Seodong folktale through a new review of archaeological and literary data. In other words, uncovering the substantial truth about the two people is the most basic task to properly understand the historical character of Iksan during the reign of King Mu in the late Baekje. As a result of analyzing the tombs and literary materials excavated in the Iksan area, it was possible to examine the deeply rooted traditional historical awareness of Mahan. In addition, it was assumed that King Mu was an outstanding political figure representing the Mahan faction, not the Baekje royal family, who grew up in the Iksan region. The Mahan faction in the Iksan region, where the perception of Mahan had been deeply rooted, became King Mu's political base and was seen as a force supporting the relocation of the Iksan capital. As a result of comparative analysis of the birth stories of King Mu of Baekje and Emperor Gojo (Liu Bang) of the Han Dynasty, it was found that both of them ascended the throne from the same status as ordinary commoners, and thus, through “the theory of the divine right of kings”, such as that the king is the son of a dragon, the consciousness of blood-related succession to the throne, a general principle in ancient society, was overcome. It guarantees the identity of Mu's succession to the throne, and its value can be found comparable to that of the founding legend. The stone pillar-shaped tombstone discovered in Sowangnung tomb has the same characteristics as Tongcheonju (通天柱), and was seen as a symbolic mark of the nature of the origin of the deceased, which originated from the Buyeo succession consciousness that greatly increased after Baekje transferred the capital to Sabi. Therefore, it was assumed that the buried in Sowangneung's tomb was a person with the same status as a princess of the Baekje royal family. It is presumed that the Baekje royal family, which fell into chaos after the death of King Seong at the end of Baekje, sought political solidarity with the Mahan faction centered on Iksan for the stability and revival of the kingdom. It is thought that this could have been achieved through the marriage of a princess from the Baekje royal family to Seodong, a central political figure in the Mahan region of Iksan. The result is believed to have been the relocation of the capital to Iksan, as can be seen from the royal palace and other capital remains, which are the requirements of an ancient capital remaining in Iksan.