Most probably not. Usually, such titles are works of fiction that draw inspiration from various sources but aren't based on actual events. It's more about crafting an engaging narrative for the audience.
It's difficult to determine the exact truthfulness. It might draw inspiration from real-life situations but be embellished and restructured to fit the storytelling format.
One theme could be redemption. The gangster has a chance to start anew in the high school environment and leave his criminal past behind. Another theme might be identity. He has to figure out who he is now, is he still the gangster or can he become a regular high school student.
I recommend "Tokyo Swordsman Head Coach" to you. The male lead, Natsuki Hanai, is very handsome. At first, he was just an ordinary high school student who wanted to play a happy otaku game. However, he later obtained many flashy titles, including the underworld dragon son-in-law, the Tokyo Swordsman Head Coach, and the king of work. He definitely fits your description of a handsome male lead and is also in the underworld. I hope you like this fairy's recommendation. Muah ~😗