Prolouge~ My ChildHood

Hiroki Fumio was an orphan and was taken in by a random ojii-san. Turns out the ojii-san was one of the largest figures in the martial arts world. The Hiroki didn't care though. That waas because every day at the orphanage's backyard he would self study everything. Including martial arts. So when the oji-san decides to test Hiroki... he get's his ass handed to him. But Hiroki wasn't perfect so the oji-san taught him techniques. He got even stronger.
One day while going back to the dojo his world a crack suddenly appears below him. He knew where this was going.
He says "Other world! Escape from school? Let's go!" He jumps straight in! What will happen to Hiroki Fumio? Well, let's follow his journey!