While Yamada was in school, he would get picked on and would transfer multiple times. When he saw one of Makunouchi Ippo's matches on TV, he became inspired as he saw Ippo would always get up and continue fighting again. Yamada wanted to become strong like Ippo, viewing him as his senpai.
Yamada was among the trove of aspiring trainees hoping to join the Kamogawa Boxing Gym after its rise to renown in Tokyo and was the only individual to persevere and make it through Takamura Mamoru, Aoki Masaru, and Kimura Tatsuya's roadwork test (albeit slowly and painfully). He was then given the nickname "Geromichi" after throwing up on Makunouchi Ippo's shirt from the roadwork. When Aoki looked into Yamada's wallet, a picture of Ippo was in it, revealing that he was a fan of Ippo. Thus, Ippo was chosen to teach Yamada the basics such as jump rope.
When the day of the Kamogawa gym's big event arrived, Yamada went to the Kōrakuen Hall, knowing that Ippo would show up and began following him. Yamada was shown the waiting room, where he was soon chased away by Aoki after taking too long to say "good luck". He was then shown the corridor that leads to the boxing ring, which Ippo then explained the reason there are glove marks on the wall. Yamada and Ippo were then met with Fujii Minoru and the JBC featherweight champion Date Eiji. After Date and Ippo had a conversation, Yamada and Ippo went to the audience seats and watched Takamura, Aoki, and Kimura's matches where all three won.
When Ippo received a sparring request against Date, Yamada went with Ippo to the Nakadai Boxing Gym, watching the spar and acting as his second. After the spar, Yamada talked with Ippo about how he used to get bullied at school and how he looks up to Ippo for being strong, wanting to be strong like him. Yamada was then shocked when Ippo told him that he had a similar past, making Yamada become moved, viewing Ippo as the "role model of all the wimps in the nation." Later, when Ippo was fighting against fifth ranker Okita Keigo, Yamada watched the match where Ippo would win by knockout.
When the Kamogawa gym had the idol, Kumiko Morita interview the boxers about their hopes in boxing, Yamada seemed to be a fan of her as he asked for her autograph. Later, after sparring with Ippo, Yamada left the gym for his Pro Test at the Kōrakuen Hall. Yamada was nervous after passing the written exam, however, he passed the Pro Test spar after downing his opponent. When he got back to the gym and Kamogawa Genji revealed the entry list for the Class A Tournament, Takamura invited Yamada to go with the rest of the gym to the annual training camp to catch up to Aoki and Kimura.
While Ippo was unable to attend the training camp due to his mother's illness, Yamada went with the rest of the gym to the training camp. He was referred to as a curse by Takamura, as Yamada's presence coincided with Kamogawa joining the troupe and a typhoon cancelling their only day at the beach. Yamada was worried that Ippo might quit boxing due to his mother's illness. When Yamada and the rest of the gym came back, Ippo was at the gym, surprising everyone. Later, while Ippo was training to defeat Saeki Takuma, he had Yamada try to hit him while Ippo used an out-boxer's footwork, which Yamada could not hit him. When Ippo was about to decide to go back to his old style, Yamada suggested otherwise and wanted him to try again. Ippo asked Yamada to put on a tougher face, causing Yamada to use a squinted look. Even though Ippo told him to not do that, Yamada's look made Ippo come up with an idea to go against Saeki. Yamada later watched Ippo, Aoki, and Kimura's matches in the first round of the Class A Tournament where all three won. Yamada then celebrated with them at the Gaiant Echo Karaoke.
After the celebration at the Giant Echo Karaoke, Yamada expressed how he admired Ippo's liver blow and wished to use it but does not know how to perform it.After Ippo demonstrated the technique for Yamada, Yamada shortly left the group so that he could go home, thanking them for everything. When Yamada got home, his mother informed him that they would be moving in two days, asking if Yamada was okay with it as he gets picked on every time they move and he would be unable to go to the Kamogawa gym. Yamada reassured her that he was okay with it, and that his memories of Tokyo will be his treasure. His mother apologised, but Yamada told her that being with the Kamogawa gym members changed him, and felt that if he got picked on again, he will be okay.
Two days later, Yamada told Kamogawa his farewells. Yagi Haruhiko informed Yamada that everyone was waiting in the basement, surprising Yamada. When Yamada entered the room, he was told to spar against Takamura, Aoki, Kimura as a farewell party. With Ippo as his second, Yamada fought against the three, ending each spar with a loss, but the three noticed the results of his training during the training camp. Ippo then got into the ring, wanting to spar for one round with Yamada to not be forgotten. Thinking that it would be his last spar with his senpai, he intended to go all out, as did Ippo. Ippo ended the spar by hitting Yamada with the technique Yamada told him he admired, the liver blow. With the farewell party over, Yamada took a shower at the gym, reminiscing at the areas he was punched at by each member that he will never forget. When it was time to leave, Yamada told everyone farewell, as everyone saw him off.
Yamada later moved to Aomori, where he joined the Hachinohe Boxing Club and continued his training. With the goal of fighting Ippo, Yamada went under the ring name, "Hammer Nao" and went to boxing gyms to fight their best fighter as an underdog. Yamada went from junior welterweight to featherweight and won all eight of his matches, eventually becoming ranked 7th in the JBC featherweights.
Two years later since his departure from the Kamogawa gym, Yamada reached his dream of fighting his senpai, Ippo, who became the JBC featherweight champion. With his short career and being ranked 7th in the JBC, he was seen as an underdog. With his title match against Ippo approaching, his coach warned him of Ippo's abilities and wondered why Yamada wanted to fight the man who brought him into boxing. Yamada expressed to his coach how knowing what he is fighting makes it easier to defeat, and that he can hit and defeat him. Yamada went from Aomori to Tokyo and transferred to the Nerima Boxing Club. After a sparring session that ended in his sparring partners throw up after a body blow, Yamada met Aoki and Kimura outside. Aoki and Kimura attempted to have a lighthearted conversation with their former kōhai, however, Yamada only provokes them with taunts and requested that they inform Ippo that he would be seriously coming for his belt.
On the day of the weigh-in, Yamada met Ippo for the first time in two years. After the weight check, Yamada declined Ippo's handshake, and thanked him for teaching him about boxing and that he was giving him the belt. Ippo responded by claiming that while they practised together, he never taught him how to take the belt. Their match arrived the next day at the Kōrakuen Hall, where, in his changing room, he expressed that despite this show of intent, it turned out to be a bluff as Yamada nearly broke down from nervousness and told his coach that he intends to retire after showing Ippo his strength.
When the match began, Yamada was overwhelmed in the first round, being knocked down thirty seconds into the fight by Ippo, who was desperate to end the fight quickly to spare Yamada. Yamada got up and clinched Ippo, who intended to do the same tactic. The clinch was quickly pushed back by Ippo, and Yamada attempted to hit him many times before getting knocked down a second time. Yamada got up and used his senpai's strategy of using the Peek-a-Boo Style and waiting for a chance to strike at the ropes as he got attacked. Yamada then sent out a body blow that got blocked and sent Ippo off his feet. Realising that body blows could land while Ippo is weaving, Yamada began throwing body blows that hit cleanly. With Ippo aiming punches at Yamada's head, Yamada hit Ippo with multiple body blows. Their exchanges ended when the referee got between them as the round ended. Yamada, irritated as their fight was just beginning, hit the ring's ropes in disappointment. In the corner, as body blows seemed to be hitting, Yamada was instructed to use the body blow that would affect Ippo: the fast reacting solar plexus blow.
In the second round, Yamada's body blow plan met a roadblock due to Ippo's tough guard blocking his body. Unable to break through Ippo's guard, Yamada demonstrated how he managed to claw up the rankings by executing subtle fouls, pulling Ippo's guard away with his hand and landing the solar plexus blow. After multiple followup attacks, Ippo recovered, leading Yamada to stop his attacks by pushing onto him with his shoulder and landing close ranged body blows. When Ippo began blocking again, Yamada used the previous tactic to open his guard, landing another solar plexus blow, immediately doing it a third time when he got Ippo to the ropes.
Yamada continued his attack after landing the third solar plexus blow, wondering how close he had come from two years ago. Ippo stopped Yamada's attack, then proceeded to open and lower his guard into the Brawling Style stance, inviting Yamada to attack. Yamada accepted the invitation and landed many clean hits on Ippo until, after many exchanges between both, Yamada was hit by a liver blow, sending him down. Yamada got back up, wanting to continue his personal world title match as long as he is conscious. Yamada could not hit Ippo, instead, got hit by Ippo's strong combinations and was sent falling, with the referee catching his fall and ending the match, resulting in Yamada's loss.
After hearing that Ippo believed that he would be stronger after his first loss when he returned to the ring, Yamada was inspired to continue boxing. Yamada and his coach then saw Ippo from a distance. The coach insisted for Yamada to properly greet him, however, Yamada believed he already had their conversation in the ring. Yamada then vowed to himself to chase the vision of Ippo's back for eternity, thanking him.
Yamada was later seen at the Hachinohe Boxing Club with trainer hand mitts and his hair beginning to grow and eyebrows when Takamura was travelling around Aomori. Locals came to ask for Yamada's help in moving an old man's truck out of a ditch. When Yamada arrived to the scene, he saw that someone had done so already. When the old man described that the man who helped was a champion with a big hairdo, Yamada remembered only one person who fits the description, but deduced that there was no way Takamura would be in Aomori.
|9||LOSS||8-1-0||1994-08-20||Makunouchi Ippo||Tokyo, Japan||2(10), 2:42||KO||"Proof of Power"|
JBC Featherweight Title Match
|8||WIN||8-0-0||1994||Unknown||Japan||N/A||N/A||Becomes Ranked 7th in JBC|
- VS Takamura Mamoru 1R KO LOSS (Farewell Party)
- VS Aoki Masaru 1R KO LOSS (Farewell Party)
- VS Kimura Tatsuya 1R KO LOSS (Farewell Party)
- VS Makunouchi Ippo 1R TKO LOSS (Farewell Party)
- VS Unknown Featherweight Boxer 1R KO WIN (Pink Shirt in anime)
- VS Unknown Featherweight Boxer 1R KO WIN (Blue Shirt in anime)
- VS Unknown Featherweight Boxer 1R KO WIN (Green Shirt in anime)
Yamada has pale skin, muscular body, long black messy hair, long moderately thick eyebrows and a large prominent nose. His eyes are large with dark coloured pupils. He has a rather meek facial expression.
When Yamada went by the ring name "Hammer Nao", he modified his appearance to that of a rugged, ugly and fearsome boxer. His head and eyebrows were shaved, his face was twisted to show a considerable amount of dimples to appear more menacing. A shadow rested over his dark eyes, and his left ear had pieces missing. Subsequent to his first loss against Ippo, Yamada began growing back his hair and eyebrows.
When he joined the Kamogawa gym, he was an extremely shy, meek and incompetent trainee at the gym, Yamada has had a lengthy history of being bullied and shunned by others for his appearance and demeanour. Nevertheless he is shown to be kind and encouraging to others and views Ippo with utmost admiration due to the latter's kind treatment towards him and their similar pasts. During his professional license certification, he bore a striking resemblance to Ippo during his own certification, albeit more stressed.
Returning with the ring name "Hammer Nao" however, Yamada's personality is viewed to have changed drastically. He is shown to be guiltless and menacing, often glaring at others and provoking them (evident in his encounter with Aoki and Kimura). He now dislikes being thought of and referred to as a kouhai and apprentice of Kamogawa gym. Yamada seems to have matured as well, and shows a good amount of seriousness towards boxing. However, he silently continues to admire and respect the strength of his former senpai Ippo.
Subsequent to his first loss against Ippo, Yamada has been shown to recover some of his former attitude and meekness, gradually reverting back to his old self.
A boxer with no particular talents to speak of, Yamada had crawled his way through his matches to challenge those of higher ranking. He fights in the standard orthodox peek-a-boo style, relying on subtle fouls during in fights to win his way through challenges. Regardless, he is a boxer shown to possess well-trained strength, endurance and spirit, and is also well known for his powerful body blows. His fight footage shows a grasp of basic boxing tactics, with Ippo noting that Yamada had learned how to read his opponent's move and use appropriate in-fighting techniques such as the Liver Blow.
Takamura mentioned that the two years Yamada had spent away from the Kamogawa gym had been spent well running, with Yamada possessing great leg power, vital for his signature body blows.
He debuted as a junior welterweight, where he fought two matches, before fighting three at lightweight, and another three at junior lightweight. Ippo notes that Yamada 'didn't know what it was like to lose' during their fight - implying he won all his matches at these weights.
Unlike many other gifted characters of the series, Yamada has no natural talent to speak of. Kamogawa describes him as an unskilled boxer. Yamada himself noted that his boxing style involves taking too many hits and predicted that his career would be a short one.
He is largely inexperienced with boxing, having never felt the pain of a loss until his match against Ippo. His movements are also (in Ippo's eyes) quite slow and readable. To compensate for this, Yamada has a tendency to perform extremely subtle fouls at close range to land his signature Solar Plexus Blow. In the final moments, Yamada executed his one-two combination and Liver Blow as he had learned from Ippo, but this was easily blocked, with Ippo returning the exact combination with damaging results, showing the gap between the two boxers.
- His nickname Geromichi comes from the Japanese word Gero, which means vomit, and -michi from his given name Naomichi. -Michi roughly translates to "path". Takamura explained the nickname as meaning "He who walks the path of vomiting".
- In an interview included as a Volume 61 extra, Morikawa mentioned - "Geromichi was based on my assistant at the time. His personality was just like that, but his face was more like when Geromichi's was when he challenged Ippo (laughs)."
- There is a Japanese boxer, Yutaka Itoi, that used the "Hammer" Ring name during their boxing career, Hammer Itoi (ハンマー糸井). He fought and lost to Hidekazu Akai at one point.