Mutou is frequently referred to as a gorilla by Minami and Hayama.
After 30 Volumes or so, Yasushi Baba begins to evolve his way of drawing muscles. It becomes more defined, shaded and solid; it coincides with the MMA Genre Shift as the characters now are mostly shirtless, and no less important, he begins to draw the women more curvy as well. Characters in particular got a beauty upgrade, Hayama and Seiji are glaring examples, their designs are completely renewed; it might be for matching looks with their beautiful girls, as they got Rika and Akiko as their Love Interests.
Imai Yuuto, a prodigy of MMA karate, experiences a taste of defeat against Minoru in the Kaburagi-ryu nationals.
Aniya Souhachi is an Old Master in traditional Okinawan martial arts, he's also an avid bodybuilder and rides a motorcycle.
Mamiya Seiji tends to get very jealous of Minoru's success with the ladies. Particularly when one of the ladies in question is a blonde.
The creepiest guy with the nightmare face: Kevin Norton. He's a bit weird looking to begin with, but hopped up on PCP in the underground fighting ring, he looks positively inhuman.
In the long run, every single main character gets a Love Interest. The girls are introduced in the very first ten Volumes (some are main characters themselves), none have competition and they were quite obvious even before becoming Official Couple. All of them are solid and have zero competition to even start a possible Love Triangle or break-up.
Haruka's use of Taekwondo - a martial art with a very high focus on kicking - while wearing a miniskirt leads to Panty Shots galore. In the same scene, she also makes sure to remove her high-heeled boots before she starts kicking: high heels are not easy to balance on in real life.
Kaburagi Karate's focus of punching people in the face is considered to be a very unorthodox tactic both in-universe and in reality. Minami explains to Minoru that the bones in human hands are much thinner than the bones making up the skull, the result being that if you were to punch someone in the head without wearing any kind of protective glove, you'd be more likely to injure your hand than your opponent. Subsequently, Kaburagi Ryu punches aim to cause nosebleeds and cuts above the eyes, rather than knock someone out.
The first time the phrase "Karate Shoukoushi" is ever mentioned in the series is in Chapter 251, when the media tries to come up with a catchphrase for Minoru. It means "The Little Prince of Karate".