The story takes place in a small city called Seigen City. On the Lion's Tail Mountain in the city, there stands a huge object shining with colorful light. This object, named "Mono's Horn", is actually the "Monster's Horn" that has been standing there since the "Monster Day" incident 16 years ago. After the "Monster Day" incident, when monsters appeared all over the world at the same time, monster disasters began to become a daily occurrence. While the Earth Defense Force of Japan began to fight monsters with force, the SKIP Scientific Kaiju Investigation and Prevention Center also continued to conduct scientific investigations and evacuation guidance in various regions in order to prevent the occurrence of monster disasters and the expansion of disasters. This organization is still investigating the cause of the "Monster Day" and the "Mono's Horn" in the city. "Yuma", who was only 7 years old, was attacked by a monster while camping with his parents on Lion's Tail Mountain. He miraculously survived and was unharmed. This opportunity led "Yuma" to embark on the path of studying monster biology. Despite his painful past, Yuma did not lose his dream. He grew up relying on the "power of imagination" and joined "SKIP" as a novice investigator and was assigned to the Xingyuan City branch. At this time, a large-scale monster disaster occurred in Xingyuan City. "I want to protect these desperate people in front of me!" The moment this strong and direct thought came out from the bottom of his heart, "Lutian", the messenger of light he had seen in his childhood, appeared in Yuma's mind and talked to him: "I am you, you are me... ... Release your imagination!" The mysterious light that appeared in his hand wrapped around Yuma's body, and the released power of imagination combined light and man, and transformed into the giant of light "Ultraman Acker" who protects the future! Yuma and Ultraman Acker, together with important partners, chase the dream that never stops, and run from now on!