Asurei Rune, also known as Supporter X, is a character from the Inazuma Eleven GO 2: Chrono Stone storyline. He is the father of Fei Rune, a key member of the Raimon team. Before the events of the story, Asurei was an officer working for El Dorado, the organization responsible for overseeing and protecting the flow of time. However, his life changed dramatically with the birth of his son, Fei, who was discovered to be a Second Stage Child, a human with latent powers that emerge from the future. Fearing that his position within El Dorado would be threatened or that Fei would lose his freedom if his nature were discovered, Asurei made the difficult decision to abandon his son. As a parting gift, he left Fei a bunny plush toy, an object that would later become associated with Fei's keshin, or fighting spirit.

Even after abandoning Fei, Asurei never stopped worrying about him. This guilt and concern drove him to take on a secret identity. He joined the organization Feida, which was composed of Second Stage Children, under the alias Supporter X. In this disguise, he wore a long white robe that covered his entire body, used a walking stick, and wore a false white beard to hide his true appearance. His true form is that of a man with short, spiky green hair and eyes, typically dressed in a white and yellow shirt with a navy blue jacket. His primary motivation for infiltrating Feida was to secretly watch over Fei and protect him from within the very organization that sought to use Second Stage Children for their own purposes.

Throughout the Chrono Stone story, Supporter X appears at critical moments, often observing the actions of the Raimon team and the antagonist Zanark Avalonic. He was present during the Three Kingdoms era, informing Zanark that his power was on the verge of awakening. Later, during the Bakumatsu era, he intervened after a match to take a Chrono Stone containing Endou Mamoru, a legendary goalkeeper, claiming that Zanark did not understand its true value. It is during this period that he is seen alongside SARU, the young emperor of Feida, to whom he provides counsel. His role becomes increasingly complex during the Ragnarok Tournament, a series of decisive soccer matches. As he watches the matches alongside SARU, his true identity begins to come into question, with characters like Gouenji Shuuya recognizing him as the one who sent a vital Time Bracelet.

The culmination of Asurei's character arc comes when he finally reveals the truth to Fei. After Fei collapses from the mental strain of conflicting demands from SARU and Supporter X, Asurei brings him to a locker room and confesses that he is his father. He explains that his abandonment was not out of fear of Fei himself, but a misguided attempt to protect him by ensuring he was not taken away by El Dorado. He admits he joined Feida as Supporter X out of worry and a desire to care for him. When Fei rejects this apology as too late, Asurei declares he will leave Feida and warns that Fei's heart will be swallowed by SARU's evil influence. This revelation paves the way for Fei to eventually reconcile with his past and with his mother, Kinako. Despite his efforts, Asurei is ultimately unable to convince SARU to stop his plans, but his actions as a father trying to atone for his past mistakes are central to his development.

In terms of abilities, Asurei is a capable player, often taking the position of midfielder. In the context of the video games, he possesses several notable hissatsu techniques, or special moves. These include Future Eye, a tactical move; Spinning Upper, a shooting technique; and Extreme Rabbit, a powerful shot. His stats in the game reflect a high technique and dribbling ability, making him a skilled and strategic player on the field.