Stay Cool, Kobayashi-san!: A River City Ransom Story

A short while after the events of “Downtown Nekketsu Monogatari”…

Reiho High School, where the battle took place, has these Big Four, who are feared by all the others schools around.
And at the top of the Big Four, reigns only one man: Masao Kobayashi. Here's one of his stories.

Back in middle school, a mysterious event led him to meet a boy named Mizoguchi, who was actually a Time Regulator, going after an evil organization that has disrupted the time-space equilibrium.

After finding out that Kobayashi has a hint of mysterious power in him, Mizoguchi has them set out together to take this evil organization down.

So, when Kobayashi's friend gets abducted by the evil organization, he puts on a calm face while burning with rage inside. He has got to go rescue his friend and bring an end to this evil organization.

Source: TheGamesDB