Before the slaughter of Yugakure, Jin Mori was born to two civilian parents of the Village Hidden in Hot Water. Jin Mori's grandfather, Jin Tae-jin, wished to take his grandson to the hot springs for the first time. During their absence, the Jashinist Hidan slaughtered his neighborhood of Yugakure before his departure, bringing "nothing less than utter destruction and death" to the families residing their, killing Jin Mori's parents. When Jin Tae-jin arrived back with a sleeping Jin Mori, he decided to say nothing of it to his grandson, and bidding Yugakure farewell and keeping Jin from danger.
After leaving Yugakure, Jin Mori went to travel the lands with his grandpa. Jin Tae-jin went to teach a form of hand to hand combat to his grandson, so in the future he may protect himself. This style was created by Jin Tae-jin himself, and was the sole user of this style until passing it to his grandson.
After years of traveling, Jin Mori, 12 years old, and his grandfather settled down in Kumogakure. Jin Mori attended the public schools here, his grandfather not allowing him to enter the Ninja Academy in fear of Jin Mori revealing his style of fighting. Yet even with this, the Raikage took interest in Jin Mori, who defeated 2 Amegakure chunin shinobi. Even with the Raikage's influence, Jin Mori refused, not accepting anyone as his sensei or master other than his grandfather. Before the Raikage could speak to Jin Tae-jin, he unexpectedly left Kumogakure, not even telling his grandson.
Without his grandfather to teach him more, Jin Mori continued to study at the public schools getting into fights to hone his skills. Even though he isn't a ninja, he still challenged trained shinobi to fights and won almost every one. The 2 he didn't win were declared ties, 1 to Rock Lee and another to an unknown person. Besides his two ties, his record went to a remarkable 300-2-0. With this under his belt, Jin Mori, now 17, was invited to a fighting tournament for non-shinobi high school students, The God of High School.