In a town called Hoshimoto City... A giant object towers in Mt. Shishio. Named "Monohorn", it is actually a kaiju's horn stuck in the ground since an incident 16 years ago. The incident when kaiju appeared simultaneously around the world was later named "K-Day." Since then, the Global Defense Force (GDF) has been dealing with kaiju with force, while SKIP (Scientific Kaiju Investigation and Prevention center) works closely with the community in scientific investigations and evacuation guidance to prevent the occurrence and aggravation of kaiju disasters. SKIP has also been investigating the Monohorn, the horn of the galactic beast Monogelos, which appeared on K-Day. Yuma, then only 7 years old, was camping with his parents in Mt. Shishio when Monogelos attacked, but somehow miraculously survived unhurt. This experience led him to pursue the path of kaiju biology research, and despite his traumatic past, he has not lost his "imagination" to dream. As a rookie investigator, Yuma joined SKIP and was assigned to the Hoshimoto City Branch. Not long after, another large-scale kaiju disaster occurs. As Yuma sees the desperate people in front of him, a strong will springs into his mind - "I want to protect them!" It was at that moment when Yuma hears the voice of Rution, the being of light that he once saw as a child: "You and I are one and the same... Unleash your imagination!" When the mystic light emerging from Yuma's hand embodies his entire body, his power of imagination fuses him with the light and he transforms into Ultraman Arc, the Giant of Light who protects the future. Alongside his precious friends, Yuma, as well as Ultraman Arc, gallops towards his everlasting dream.