Mondo grew up with his older brother, Daiya Owada. He owned a Maltese dog named Chuck who he loved deeply. Chuck used to bring in the newspaper every morning when it was delivered to Mondo's home and would always beg Mondo for walks each day but died at the age of nine sometime during Mondo's childhood. He was raised by his brother to become strong and mentioned that his mother would kill him if he were ever to hit a woman.
He became dedicated to biking when he was young, being first allowed to ride with The Crazy Diamonds through his older brother Daiya Owada who invited him into the gang. Mondo was inspired by his older brother to take up biking and helped continue to transform The Crazy Diamonds into a well-known biker gang. From then on both brothers were known as The Diamond Brothers, a well-known name across Japan. Mondo constantly lived in Daiya's shadow. When he first began riding he ended up at the back of the group which ended in him being caught by the police, causing a scuffle. Despite this Mondo was still able to rise through the ranks with perseverance and patience. Mondo became the second leader of the Crazy Diamonds, after his older brother Daiya at which time the group was now Japan's fiercest and largest Biker gang. When it came for the day Daiya would retire and hand over leadership to his younger brother, Mondo challenged him to a race on his retirement party to prove he was worthy to take the helm after the gang members refused to put their trust in him. However during the race Mondo became reckless and went head-on into oncoming traffic, Daiya pushed Mondo's motorcycle aside in place of his own to protect him and ended up dying in a collision with another vehicle. Despite Mondo being devastated, it was Daiya's final wish that he continues to lead the Crazy Diamonds and not blame himself for the accident. Mondo did not tell the gang members that he caused his brother's death and continued to maintain the Crazy Diamonds as the best gang in Japan. Mondo attended First Volcano High School, nicknamed "Scum School" due to the high rate of delinquency and fighting.[5] He was later scouted by Hope's Peak Academy as part of Class 78th which he accepted, the reason for this being that he was escaping the fear of losing the Crazy Diamonds, something that had been a constant part of his life. After keeping his gang at the top, Mondo felt the need to look for other aspirations as the other gang members intended to do upon graduating from The Crazy Diamonds and High School themselves. It is implied Mondo made the head of the elite guard for the Crazy Diamonds Takemichi Yukimaru the interim leader of the gang during his time at Hope's Peak Academy, as his most trusted and closest friend following Daiya's death he believed this was the correct replacement.
