Holyland is a fairly realistic martial arts-based series with footnotes on how any used or subverted trope fits in with how martial arts really work.
Meet Kamishiro Yuu, a young high school student who was bullied during middle school. The harassment gets to the point he stops going to school and starts secretly training to fight. A year later, disconnected from life around him, he has taken to roaming the streets looking for a place to belong.
He unleashes his secret left-right combo on random street thugs and in doing so gains a reputation as a thug hunter. He ends up fighting increasingly strong opponents as everyone wants to test his skill. Though the series deals a little with the reality of gang violence, people beaten into comas are usually out of the hospital in a few chapters.