Yagbe'u Seyon served as co-ruler with his father Yekuno Amlak for the last few years of his reign, which eased his succession. A Memorandum in the Four Gospels of Iyasus Mo'a of a gift of vestments and utensils to Istifanos Monastery in Lake Hayq states these gifts were in the name of both Yekuno Amlak and his son Yagbe'u Seyon. He sought to improve the relations of his kingdom with his Muslim neighbors; however, like his father, he was unsuccessful in convincing the powers in Egypt to ordain an abuna or metropolitan for the Ethiopian Orthodox Church. A letter from him to the Sultan of Egypt, dated Ramadhan A.H. 689 is mentioned in Etienne Marc Quatremère's Mémoires géographiques et historiques sur l'Égypte… sur quelques contrées voisines, where he protests the Sultan's treatment of his Christian subjects, stating that he was a protector of his own Muslim subjects. Marco Polo mentions that one of the "princes" of Ethiopia planned in 1288 to make a pilgrimage to Jerusalem, following the practice of a number of his subjects; he was dissuaded from this project, but sent his "bishop" in his place. On his return leg, this bishop was detained by the "Sultan of Aden", who attempted to convert the ecclesiastic to Islam; failing to do so, the sultan then had the bishop circumcised before releasing him. The "prince" then marched upon Aden, and despite support from two other Muslim allies, the sultan was defeated and his capital captured. A number of historians, including Trimingham and Pankhurst, identify the ruler with Yagbe'u Seyon, correct Polo's reference to Adal not the Arabian seaport, and name Zeila as the sultan's capital. Another incident during his reign was the revolt of Yi'qebene, who attempted to take the Imperial throne from Yagbe'u Seyon. This threat is recorded in Yagbe'u's own words in a note he wrote in the Four Gospels of Iyasus Mo'a: Historians are divided over the situation that his successors faced following Yagbe'u Seyon's death. Paul B. Henze repeats the tradition that Yagbe'u Seyon could not decide which of his sons should inherit his kingdom, and instructed that each would rule in turn for a year. Taddesse Tamrat, on the other hand, records that his reign was followed by dynastic confusion, during which each of his sons held the throne.
