Dexter Kassah, is an amateur photographer on Earth. Well, on his "Earth," that is. It was then that night that changed his life. When he was out trying to get beautiful photos of the stars and constellations. He witnessed a spaceship crash nearby, he investigates it and finds a dying alien named Tsuya. He doesn't tell him where he's from, but all he did tell him was about the Deca Belt and the instructions to "Find the Riders, Earn their Power, Become Deca!" That was all Dexter got before the Alien passed. He had to find someone to tell about this, but the only people he thought he could trust were a friend and her brother. He was looking through the ship, and they found it had the power to harness Deca's ability to travel to other Earth's, causing the brother to be excited as he wanted to pilot it. So this is where their journey began.