Hayama Kentarou is introduced as a caring, comical, and all-around weak first year college student at Reinan University. He is in the Second Karate club, who lets Minoru move in with him. With this act, he unofficially becomes Minoru's first friend.
At the start of the manga, Hayama is shown have medium brown hair (down to neck) and full round lips. He was considered to be quite ugly. After the art evolution by Baba Yasushi, his face is a little longer. With longer brown hair (down to his clavicle). His lips, while still big, aren't necessarily protruding out out as to when he was first shown. He has wavy medium length sideburns. Thin full length eyebrows.
Hayama is shown at the beginning of the story as the weakest and all around lamest member of the Second Karate Club. Hayama has had low self-estem issues since he was the weakest out of the club. He says every time he gets hit their face starts to look like "his". Since Kentarou was bullied out of the Karate-Do club after a week, "his" could be referring to one of the first karate club's senpais.
As the story progresses, he inevitably grows into one of the greatest karateka, fighting in tournaments. Kentarou talks extremely high of himself, ironically he doesn't believe in his strength until Ragnarok. He still has a knack for saying lame things at times. Recently Kentarou has started to believe in his own strength, and still talks big, even though he's still the weakest out of the troupe (Minoru, Mamiya, Hayma).
Unexpectedly he's more persistent than the other members when it comes to dealing with the opposite sex. In the beginning, he always asks Minami Hiroki to take him out on his group dates. And to this day harbors small resentment for the fact that his former captain has never taken him once. Hayama is also the second member of the second karate club to get a girlfriend. He is also a little perverted, as he has a sharp porn memory and has a ton of adult videos/magazines-assuming until he and Rika became a couple. Most likely still has them, the proof is just hidden.
One of his best friends-kinda like brothers (other being Mamiya). Usually spars with him the most. Usually, and kinda oddly, speaks sense to Minoru when he's worrying about a match or fighting a dangerous opponent. He also recognizes and respects Kohinata's strength (sometimes he will say the opponent is too strong and leave it to Minoru). It's one of his goals to catch up to Minoru.
Other one of his friends (brothers). They have an apparent rivalry that goes from arguing over abilities/strength to arguing over little things.
Dorm roommate that he and Minoru are super terrified living with. He's apart of the club so Hayama considers him an ally. Since his past is questionable, Hayama and Minoru (mostly Minoru) have been on guard desperately learning counter ground pinning techniques (only Minoru has been able to perform it)
Hayama's girlfriend. After the first trip to Okinawa, She taught him some katas and first discovered his ability. And then made him promise to teach her karate (not seriously teach her, but become strong). In chp.93 they formed a relationship and since she got accepted to Reinan during the time-skip, they've been together and ever since.
Hayama is extremely proficient at kata. He says he is only good, because it doesn't hurt like kumite (real sparing). Even with this, he still has the worst aptitude among all the members. And he has no guts at all. This has most likely changed after the Ragnarok tournament.
Kentarou has high sensitivity- meaning he can envade an attack/or something coming at him, even without him actually seeing it with his eyes (surprise attacks/feints won't work on him). And because of his ability and Pedro's training, ground techniques (of Pedro's level) or lower won't work on him anymore. Since training in this ability his defense has gone up some levels.
He stays a white belt in Kaburagi-ryu karate while Minoru and Mamiya graduate to green belts. In Chapter.166, he is a 3-kyuu purple belt. In Chapter. 237, Hayama, Minoru, and Mamiya become 1-dan Black belts. It is later revealed that Kentarou failed the 10-Man Kumite, and would've failed his promotion test, but Tachibana and Akita took a little pity and gave him credit for his Kata scores.
- He refers to himself as a "Kata Genius"