Hello fellows,
I have trouble remembering a manga or oneshot shounen/seinen title. It is about a kid who is witness of several bully. He grows up and each times find excuses for not helping.

First panel, as a grade schooler, he doesn't help because he thinks he is not strong enough, and that when he will grow up, he'll be able to help.
Second panel, another bully scene happens, as a middle schooler, he doesn't act either, for same reason.
Third panel, another bully scene, as a high school student, perhaps in a train...

Then he made up its mind, thinking about courage. He discovers that true courage, is not about power, but about acting, fighting without knowing beforehand, whether he will be successful or not.

Thank you very much for your help.