I want to hit more than 30 home runs and win the home run title.

These are the words of Koki Yamaguchi, who expressed his enthusiasm at the new player announcement event held eight years ago on December 4th, and who has grown into a true long-distance slugger by hitting 38 Home Runs this season.

The man, who has set a goal of 30 Home Runs every year since turning professional, expressed his joy at reaching the milestone for the first time by saying, 'I am happy.' This marks a historic achievement for the first time in 40 years, as no Japanese player for the club had hit 30 Home Runs in a season since Hiromitsu Ochiai hit 50 Home Runs in 1986.

Yamaguchi hit three consecutive Home Run in a game against the Orix Buffaloes on September 22nd, leading the team with 16 Home Run that year. Last season in August, he tied a Pacific League record by hitting Home Run in four consecutive At Bat. While he hit impactful Home Run and would occasionally produce them in large quantities during the season, his challenge was to hit them consistently.

In a press conference following last year's contract renewal negotiations, he shared his self-analysis on what is necessary to continue hitting Home Runs throughout the season: 'I think the mental aspect becomes important. I believe everyone feels this way when they are hitting well, but when you are on a roll, you feel like you can keep hitting. When you start to feel tension somewhere or start overthinking what you have to do, I think it's difficult to get good results. So, I believe how calmly you can stand in the batter's box becomes crucial, and beyond that, I think it's just a matter of practicing.'

Regarding the "feelings" and "switching gears," when he met mixed martial artist Hiroya, he asked him about how to switch gears. Hiroya gave him the advice, "Everyone gets depressed sometimes. What's important is how you act afterwards!"

During voluntary training in January, hard training sessions were conducted at places like Zozo Marine Stadium. Reflecting on the February camp in Miyakonojo, the player said, 'I'm glad I was able to finish it in good shape without any injuries,' and expressed enthusiasm, saying, 'I want to hit for extra bases, and I think it's necessary to keep hitting them consistently rather than just aiming for them. Since there is a possibility I won't just be a first baseman, I'll prepare for both. First, I think I have to make an appeal with my batting.'

"I think it's important for me to live each day without regrets, so I'll do my best to prepare for the games and hopefully get some results," he said, expressing his determination as he entered the exhibition games. In a practice game against Yakult on February 15, in his fourth at-bat in the bottom of the ninth inning with no outs and no runner on base, he hit a massive home run to left field off the second pitch, a fastball thrown by Shoji Kota after a 1-ball count. Then, in a practice game against Hanwha of Korea on February 22, he had a spectacular performance with 3 hit 4 RBI. Even after the open season began, he continued to impress for the opening of the season with 2 hit and 1 RBI in a game Rakuten Eagles on March 5.

In an interview on March 14, Yamaguchi muttered, "It's been a mixed bag, I guess." When asked about his good performance in the March 7 game against Nippon-Ham, where he hit doble double to right-center field off a 140 km/ cutter thrown by Tamon Asari on the second pitch of his first at-bat in the second runner with no outs and no runners on base, he showed his determination by saying, "I'm continuing to do what I've been working on in training camp. I think all I really need to do is produce results in games."

He grabbed the first team for the opening day of the season and appeared starting line-up in the 4th position first baseman against Softbank Hawks on April 3, but was removed from the first team roster on April 19. After his demotion to the second team, he appeared in 15 games and had a .300 batting average, 3 Home Run and 6 RBI, when Kyota Fujiwara, a player of the same grade, left the team due to injury. Replacing Fujiwara, Yamaguchi returned to the Ichigun on May 12.

He immediately appealed with his bat. starting line-up On the same day against Nippon-Ham, he appeared at the plate in the 6th position in left field, and with 0-0 in the 2nd inning and no outs runner, he hit a 151 km fastball pitch, the third pitch Hiromi Ito he threw from 1 ball 1 strike, back to left field and lit up the "H" light in his first at bat after his promotion.

The following day, in the game against Nippon-Ham on the 13th, in the 7th inning with one out and a runner on second base, he came to bat for his third time and said, "I didn't think it would go in, but I'm glad. I'm happy. I'm really happy that I got a result." He slammed the fourth pitch, fastball thrown by Ren Ren Fukushima with a 2-ball, 1-strike, into the front row of the left field stands for his first home run of the season, a two-run shot.

In the first at-bat with no runners out in the second inning of the Seibu Lions game on May 20th with the score at 0-0, he hit his second solo home run off the seventh pitch, a slider thrown by Shinya Sugai on a 1-ball 2-strike count, saying, 'I'm glad I could take the lead.' In the second at-bat with one runner out in the fifth inning of the Rakuten Eagles game on May 22nd with the score at 1-1, he hit a decisive third solo home run into the left-field home run lagoon off a 151 km/h fastball thrown by Daichi Shibata on a 1-ball count, saying, 'It was perfect! It's thanks to Masunosuke. I had it at the sushi restaurant Shota Suzuki took me to yesterday!'

Furthermore, the following day, on the 23rd, he hit a solo home run for the third consecutive game against Rakuten Eagles, and then on the Rakuten Eagles, in the 9th inning with no outs and no runner on base, in his fifth at-bat, he hit a 152 km/h fastball, the sixth pitch thrown by Shoma Fujihira with a 2-ball, 2-strike, into the left-center field stands for his fifth solo home run, his fourth in four consecutive games. In that game, he showed the remarkable feat of hitting four hit in a single game.

Even after the interleague games began, in the game against Hiroshima on May 27, he said, "I felt good hitting in my first two at-bats, but I couldn't get on base, so in this at-bat, I was thinking about getting on base as the leadoff batter. I'm glad that it worked out well." In his third at-bat in the 6th inning with no outs and no runner on base, with the score 0-2, he hit slider thrown by Shohei Mori on a 1-ball, 1-strike count into a solo home run to the foul pole, his 6th of the season.

He responded with results to the opportunity that came his way due to Fujiwara's injury. In the game against the Hanshin Tigers on May 31st, during his third at-bat in the 8th inning with one out and runners on first and second in a 2-2 tie, he hit a decisive two-run RBI double to right-center off the fifth pitch, a 134 km/h outside slider thrown by Moreta after a 1 ball 2 strike count. Then, in the game against DeNA on June 14th, during his third at-bat in the 5th inning with two outs and the bases loaded in a 2-2 tie, he demonstrated his clutch hitting in a critical moment by driving a fourth-pitch change-up from Yuya Sakamoto after a 1 ball 2 strike count for a game-winning two-run RBI hit, saying, 'It was all about spirit.'

In the game against the Rakuten Eagles on June 21, during the first inning trailing 0-1, Toshiya Sato's RBI hit tied the game. Then, in his first at-bat with two outs and runners on first and third, he said, 'I'm glad I had the chance. It's thanks to Toshiya-san (Sato) for running hard,' as he hit the fourth pitch, a fastball thrown by Masaru Fujii on a 2-ball 1-strike count, for a 2-run RBI doble over right field. In his second at-bat in the third inning with one out and runners on first and third while leading 3-2, he hit a 148 km/h fastball thrown by Uchi Seiryu on a 1-ball count for a sacrifice fly to right field.

In his fourth at-bat of the game—with the score tied at 4–4 in the eighth inning, no outs, and a runner on first—Ren Kajiya, after a ball, threw the second pitch, a fork, which Yamaguchi sent soaring into the left-field stands with a “typical Yamaguchi” rocket line drive. This marked Yamaguchi’s first double-digit home run Home Run in three years.

In an interview after pre-game practice, he said his batting was "normal," but in the post-game hero interview, he emphasized, "I think my batting is good."

Hitting back the fastball, which was a point of concern.

He firmly hit back the fastballs exceeding 150 km/h, which had been a challenge for him. In his first at-bat with one out and no runners in the second inning of the scoreless game against DeNA on June 12, he hit his 8th solo home run to the center-field screen off a 153 km/h fastball thrown by Taisei Irie on a 2-2 count. Then, in his second at-bat with one out and no runners in the fourth inning of a 1-1 game against DeNA on June 14, he hit a doble to right-center off a 156 km/h fastball thrown by Shuto Ogata on a two-strike count, demonstrating that he is no longer being overpowered by strong fastballs.

When asked about the reason, Yamaguchi said, "I feel like I've changed my stance and am now able to swing smoothly without unnecessary movement or force," and explained, "It was a challenge for me, so I think the fact that I'm hitting well in that regard is why I'm maintaining a high batting average."

Hitting coach Kenta Kurihara also praised Yamaguchi's hitting, saying, "He's been able to hit fastballs with more power this year, so I think that's a real sign of his growth." He continued, "He was always good at hitting breaking ball and half-speed pitches. Now that he can hit fastballs, his range has broadened, and I think he has more composure at the plate."

Yamaguchi had spoken about "switching gears" mentally during his self-training in January, and since the season started, he has said, "I think I'm doing that properly. I'm trying to move in a positive direction and not a negative one," showing that he is approaching baseball positively every day.

"I think it's been working out well so far," he said, suggesting that his ability to control his mental state is one of the factors contributing to his good results.

In addition to his mental growth, he never neglected his preparations to achieve results, such as silently practicing long tees from the third-base dugout toward the left-field pole before team practice. He became able to hit back 'fastballs' and learned how to switch his mental state, becoming more resilient. Previously, his challenge was the large fluctuations between his good and bad spells, but since being promoted back to the first team on May 12th, he has displayed stable hitting for over a month. While evolving from a 'promising power hitter' into a 'genuine power hitter,' his momentum has accelerated even further since July.

◆ Season personal best for Home Runs as of July

Even after entering July, although there was a period in early July where no Home Run was hit, he consistently reached base by recording hit and Walk. After hitting his first Home Run since the June 30th game against the Rakuten Eagles in the July 15th game against the Seibu Lions, he hit Home Run in three consecutive games starting from the July 20th game against the Softbank Hawks. By hitting his 15th Home Run in the July 22nd game against the Rakuten Eagles, he reached the halfway point of his goal of 30 Home Run.

Don't worry about it too much. I feel like I'm doing what I need to do when I'm in the game. A home run isn't the only way to contribute, so I just hope to keep hitting and contributing in every game I play.

In the game against the Orix Buffaloes on July 24, during his first at-bat in the first inning with one out and no runners on and the score at 0-0, he hit a 149 km/h fastball thrown by Teranishi on a 2-ball, 2-strike count. The moment he hit it, everyone knew it was gone as he launched his 16th solo Home Run of the season into the left-field stands, tying his personal season high. Then, in the game against the Orix Buffaloes on July 26, during his first at-bat in the first inning with one out and no runners on and the score at 0-0, he said, 'I was able to hit it just as I planned,' as he drove the sixth pitch, a change-up thrown by Alen Kuri on a 3-ball, 2-strike count, into the upper deck of the left-field stands for his 17th solo Home Run. In the blink of an eye, he set a new personal record for Home Runs in a single season.

Mass Production System

I think it turned out to be a month where everything went exactly as I had hoped.

In August, he entered a mass-production phase. After reaching his first season milestone of 20 Home Run during the Softbank Hawks game on August 11, he hit Home Run in four consecutive games from the Rakuten Eagles game on August 18 to the Nippon-Ham game on August 21. With a walk-off home run against the Softbank Hawks on August 26, he tied Inoue's record of 24 Home Run in a season. Then, during the Softbank Hawks game on August 27, he stated, "I was able to surpass Seiya-san's (Inoue) total and catch up to Hatsushiba-san, so next I will do my best to aim for Ochiai-san's total," as he cleared 25 Home Run in a season, tying the record for the most by a Japanese player since the move to Zozo Marine Stadium.

In the match against Nippon-Ham on August 28, he hit his 26th Home Run, the most in a single season by a Japanese player since the move to Zozo Marine Stadium. He hit 10 Home Runs in August, earning the monthly MVP award and becoming the number one batter in the Pacific League for August.

I didn't really think I would be chosen, so I'm happy. I believe that if I can keep this up, those kinds of titles will come into view. I want to make sure this isn't just for a short period, but something I can sustain.

Even after entering September, in the game against the Rakuten Eagles on the 8th, during his fifth at-bat in the 9th inning with one out and runners on first and second in a 2-2 tie, he hit a 146 km/h fastball on the fourth pitch thrown by Naoto Nishiguchi after a 2-ball 1-strike count for a timely doble over the center fielder, marking his third walk-off hit of the season.

In the game against Nippon-Ham on the 15th, after hitting his 29th two-run home run in the 6th inning, he stepped up for his fifth at-bat in the 9th inning with no runners on and the score tied 6-6. On the fourth pitch, a fastball thrown by Taisei Yanagawa with a count of 2 balls and 1 strike, he hit a game-winning solo shot into the left-center stands. This marked Yamaguchi's first time reaching 30 Home Runs in a single season. 'It has been my dream since entering this world, so I am glad I could achieve it,' he said with a smile. He added with determination, 'I felt a strange pressure on myself when I was just a bit away from 30, so I am glad I could reach it early. I believe I can aim for the home run title if I keep improving my form, so I want to do my best to reach that goal.'

In the game against the Rakuten Eagles on September 17th where he played as the leadoff hitter, during his first at-bat in the first inning with no runners out and no one on base and the score at 0-0, he said, 'It's my first leadoff home run since that one time in the Phoenix League. Genki (Ishigaki) worked hard, and I just rode that good momentum.' He hit the first pitch, a fastball thrown by Tatsuki Koja, into left field for his first career leadoff Home Run. In the game against the Orix Buffaloes on September 22nd, he remarked, 'I felt good hitting that. I didn't think it would go out, and I didn't even realize it had gone over. I'm really frustrated that we lost the game, but I'm super happy about the home run.' During his fifth at-bat in the ninth inning with two outs, no runners on, and the score at 3-6, he hit Machado's first pitch into the center field screen for his 32nd solo home run.

In the game against the Softbank Hawks on October 3rd, which was Yuki Karakawa's retirement game, he said, 'I'm glad we won. I think we were able to send Karakawa-san off in a great way!' In his fourth at-bat in the 9th inning with the score tied 1-1 and no runners on, he hit the first pitch, a 155 km/h fastball thrown by Yuki Matsumoto, into the center-field screen for his 35th walk-off home run.

In the game against the Rakuten Eagles on October 4th, during his second At Bat in the fourth inning with no outs and a runner on first while trailing 0-1, he turned on an inside 140 km/h cutter thrown by Takahisa Hayakawa on a 2-ball, 2-strike count for his 36th solo Home Run. He commented, "I hit it well. I was able to take the lead for the most Home Run on the Chiba Lotte Marines! I will keep adding to it. I'll do my best!" This marked the most Home Run in a single season since the move to Zozo Marine Stadium, as well as his 19th Home Run of the season at Zozo Marine Stadium, setting a new record for the venue.

Ultimately, he increased his Home Run count to 38, and in the final stages of the season, he appeared in the 1st and 2nd batting order spots, reaching the required number of plate appearances. In this, his 8th season, he played in 113 games and became a true long-range slugger with a .277 batting average, 38 Home Runs, 81 RBI, an OPS of .931, and a .329 batting average with runners in scoring position.

He made the most of the promotion opportunity that came his way due to Fujiwara's injury, and there is value in the fact that he seized it. 'I wouldn't say whether it has value or not since it was due to someone else's injury, but I do think I was able to grab the opportunity.'

This season, in addition to becoming able to hit back fastballs, he was also able to judge pitches better, and his consistency improved, such as reaching base in 27 consecutive games from the DeNA game on June 14th to the Nippon-Ham game on August 2nd. 'It became a good season like never before, and although there were various slumps, it was also good that I was able to keep those slumps small,' he said.

Furthermore, his batting average from the third plate appearance onwards was .320 (66-for-206) with 22 Home Runs, showing an improved ability to make adjustments during a game. Reflecting on this, he said, 'That's part of it. I had various approaches in my repertoire, and I think I was able to utilize them effectively.'

Batting coach Kurihara praised him unreservedly, saying, 'I think the biggest change is that his timing and swing have become compact and simple. Up until last year, his swing was what you might call large; because the swing duration was long, there was a high probability that he would swing at pitches outside the zone. This year, his plate discipline has improved significantly. I believe he reached those numbers because he was able to capitalize on pitches over the heart of the plate. I think he is showing tremendous growth.'

Yamaguchi has been selected for the Japan national team for the 'RAXUS Asia Professional baseball Championship 2026' starting on the 12th, and his battle is not over yet. The manager of Samurai Japan is Tadahito Iguchi, who led Lotte for five years starting in 2018. Yamaguchi also played under him for four years starting in 2019. He is looking forward to it, saying, 'I am happy to be able to work with him again.' He hopes to conclude the final battle of 2026 on a high note.

Interview and text by Yuta Iwashita