
Born to a couple in the Fuuma Ninja village (located somewhere in the Kanagawa Prefecture) during the Bakumatsu, he's one of two children born the same day. Upon the day him and his older twin brother were born, the clan head of Fuuma, the current Fuuma Kotarou, ordered the twins' parnts to kill the younger brother. Because since ancient times, twins has been seen as taboo, and as something unnatural and vile. Humans are not animals, and should therefor not get more children at the same time, since it's an abomination.
However, the twins' parents only pretended to kill their younger son, and instead, they locked him deep inside a dark and lonely cave, where he was reared in secret. The boy grew up wanting nothing more than to be able to walk freely outside the cave, as well as become a proper, actual Fuuma shinobi.
Over the years, his older brother taught him how to fight, and sometimes, he snuck out of the cave to train by a pond together with his brother. This always ended up with them getting scolded by their parents, however, because if he left the cave, than meant that he risked being seen by someone from the village, and that would be really bad.
One day, his brother went through the coming of age ceremony, to become an actual Fuuma, The ceremony meant that you had to kill someone cose to you, like a family member. His brother killed their father, and since then, their mother stopped smiling at the older brother.
The years passed much the same, and his older brother became one of the village head's favorites, and a candidate for the next Fuuma Kotarou, despite his young age. During the time, people were displeased over the tradition of killing ones family, because not only was it a traumatic experience that turned their hair white and their eyes violet, but with the clan detoriating, they couldn't actually adfford all the deaths. At the same time, the younger members of the clan wanted to find the Orochi, a great serpent that revives every 300 years to spread chaos across the land. The Fuuma clan has served the Orochi for generations.
One day after their mother had found them practicing at the pond, she informed his older brother that the clan head had called the head candidates to a meeting. After that meeting, while his brother was meeting with friends, the clan found him, and dragged him out of the cave. The clan head was trying to force their mother to kill her younger son, but when she refused, he tortured her in front of her child's eyes. The elder then set her on fire, and when he pushed her down a cliff, the boy dove to catch her, finally breaking free from the arms that held him back. He didn't want to let go of her even when he started to burn, too. His older brother cut off her arm to make his brother let go, and that was the first time their mother smiled at the older brother since the death of their father.
Half the boy's body was badly burned, and fainted from the pain. While he was out, his brother's friends were killed by the clan head, and his brother cut off the clan head's head. When he managed to move, the younger brother hit one of the village's older shinobi in the head and the twins proclaimed themselves the new Fuuma Kojirou.