Change 123 follows Motoko Gettou, a not-so-average teenage girl. Orphaned at an early age after the death of her mother, she was taken in by her "three fathers," each a master of a different style of martial arts or combat-training. Under the care of each parent, a young Motoko was subjected to excessively rigorous training. So much was the physical and mental strain that Motoko developed three split-personalities, known as the HiFuMi, consisting of the ever hard-headed Hibiki, quick and agile Fujiko, and cute and immature Mikiri, each individually skilled in combat skills learned from each master. One day, a man begins to harass a terrified Motoko, now in high school, as he catches her alone down an alleyway. A classmate of hers, Teruharu Kosukegawa, tries to help Motoko, only in time to watch as an infuriated Hibiki kicks the harassing man directly across his path straight into a car. Returning to herself, a shocked Motoko promises Kosukegawa she will do anything if he doesn't tell her secret. From here poor Kosukegawa must manage a flurry of combat fighting and ecchi madness as he is brought along for the ride of his life into the chaotic lifestyle of HiFuMi. But what initially developed as a friendship seems to have become more to Kosukegawa as he longs to tell Motoko his feelings for her -- if he can manage to survive long enough to confess, let alone find the opportune moment. What will transpire?
In Change 123, we meet Motoko, a girl with a very strange problem. In order to cope with her 3 adoptive fathers' incredibly intensive training methods, she developed multiple personalities, each with a different martial specialty. But what happens if none of them can beat her opponent on their own? And what further nugget of wisdom will be imparted by the great Kamen Raider?