A Past Where He Caused His Wife to Worry… Lotte’s Koki Yamaguchi Talks About the Mental Shift Behind His 38 Home Runs and His Big Goal for Next Season
Chiba Lotte’s Koki Yamaguchi (26) finished last season with seven home runs but hit 38 this season—second in the league. In Part 1, he discussed the reasons behind his breakthrough, explaining how he refined his batting form by studying Teruaki Sato’s hitting videos and focused solely on “hitting the ball hard.”
In this second part, we’ll hear about his mental growth, time spent with his family, his thoughts on his first selection to Samurai Japan, and his determination to win individual titles and lead his team to a championship next season.
I really put my wife through a lot
The more he excels, the more he becomes the team’s cornerstone—and the greater the pressure and inner conflict. Reflecting on the past, Yamaguchi opens up about his mental game.
“Up until last season, I’d often get frustrated and take it out on things, and there were plenty of times when I’d come home in a bad mood. I was terrible at switching gears. I can’t say I’m that good at it even now, but I’ve gradually gotten better at turning negative energy into positive—even if it’s just a little at a time.”
Although things are different now, he admits there are still days when he can’t hit and he gets down. However, by resetting his mindset every day, he’s stopped letting negative thoughts linger.
“Even if I hit well in the previous game but didn’t get the results I wanted, I’d reset my mindset and approach every game with a fresh attitude, thinking, ‘I’m going to hit today, I’m going to hit today.’ I come here every day to produce results, and I was only looking up. I think I was able to maintain a strong drive to improve.”
This mental growth has boosted his performance. And now, even at home where his beloved family awaits, he says he tries to “stay cheerful at all times.”
“Honestly, I feel like back then, even when I got home, I was kind of like a shell of myself (laughs). I’d come home quietly, with low energy… Looking back now, I realize I really made my wife (former AKB48 member Aika Tada, 31) worry. Now, I make a conscious effort to be cheerful.”
As he battles through a grueling season, his personal way of unwinding is relaxing at home—and dining out with his wife and their 2-year-old daughter.
“I like having time to relax at home. And eating out with my family, too. During the season, since my child is still small, we don’t insist on fancy restaurants—we just eat at ordinary family restaurants nearby. If my child says, ‘I want sushi!’, we go to ‘Hama Sushi,’ and we go to ‘Saizeriya’ all the time, too.”
Looking back, during the game on May 10, the team’s leadoff hitter—Kyota Fujiwara (26), who joined the team the same year as me—was injured and sidelined. When the team was struggling, Yamaguchi, who was called up from the farm team, instantly became the fans’ “beacon of hope.” Even while shouldering all those expectations, he himself remains remarkably calm.
“I don’t feel any pressure at all to ‘live up to the fans’ expectations.’ I’m just playing with the simple desire to produce results. That said, when I hit, they cheer for me, and when I miss, I get a lot of flak (laughs). Lotte fans are passionate and intense. But I’m really happy that people are paying attention to me.”
In addition to the passionate cheers from the stands, there’s something else at Lotte’s home stadium, “ZOZO Marine Stadium,” that gives Yamaguchi a boost: its unique “wind.”
“At Marine, the sea breeze sweeps through the stadium, so the ball travels farther when hit low. On the other hand, if the ball goes higher than the stands, it gets blown back, so if I hit it too high, it won’t go in.I’m not really the kind of hitter who hits with a high trajectory like a home run artist; I’m the type who hits low, line-drive shots that carry straight into the stands. That’s why I’m able to make good use of the wind at Marine.”
He fell two home runs short of the home run title, which went to SoftBank’s Ryoya Kurihara (30), who hit 40. When asked about figures who inspire him or his rivals, he names some of the Pacific League’s most powerful sluggers.
“I was always keeping an eye on Mr. Kurihara’s home run total. It was tough, though… Another thing that catches my attention are my peers on other teams. Nippon Ham’s Manami (Nakamasa, 26) and Nomura (Yuki, 26) entered the pros with me right out of high school; they’re both right-handed batters with similar styles. I’m definitely keeping an eye on those two.”
I wanted to be called up to Samurai Japan.
As a key player on the team next season, he is expected to perform well right from the opening game. Although he played primarily as a designated hitter this season, when the topic turns to defense, he reveals his honest, unvarnished thoughts.
“I definitely think it’s better to be good at defense. But if you ask me if I’m going to get a lot better from here on out, I don’t think so (laughs). I play both left field and first base, but for me personally, they’re pretty much the same. To be honest, I don’t really want to play defense.”
Yamaguchi says this with a wry smile, but behind his words lies the “determination” of a home run hitter.
“I think the designated hitter is a legitimate position in its own right. If I can keep putting up these kinds of numbers every year, I’m confident I can compete for the position against foreign players and others. I can only earn my keep with the bat. I’ll prove myself with the bat.”
Yamaguchi was selected for “Samurai Japan” for the first time for the “2026 Asia Professional Baseball Championship” to be held in November. When asked about his feelings regarding the Japanese national team,
“I’d never really thought about it at all. Even now, I don’t think I’ve reached that level yet. But of course, I’ve always wanted to wear the Samurai Japan uniform. I’ve never been selected for the Japanese national team since I was a kid, so I wanted to slip it on at least once,”
he said, revealing his joy at finally achieving his long-held dream of making the national team.
He has achieved the 30-homer mark, a goal he’s had ever since turning pro. With his sights set on new goals, his focus is now on next season.
“Next season, I want to easily clear the 30-home-run mark and win either the home run title or the RBI title. As for RBIs, I had 81 with 38 home runs this season, so I should be able to drive in even more. This season, I batted second a lot to reach the required number of at-bats, which resulted in many solo home runs.
Next year, if I can hit even better in the cleanup spots—like the third or fourth spot—I think I’ll consistently come up in key situations since Fujiwara and Nishikawa (Fumio, 23) are batting ahead of me, and I should be able to contribute even more to the team. I really want to win the championship with the Chiba Lotte Marines. That is my number one goal.”
The day is drawing near when this right-handed Japanese slugger, who has been breaking the team’s home run records one after another, will become one of the central figures in Japanese baseball.
[YouTube] On FRIDAY TV, in an episode titled “[Exclusive Interview!] Chiba Lotte’s Koki Yamaguchi: ‘This Is How I Hit Home Runs at ZOZO Marine!!’”In this episode, the “Makuari Slugger”—who blasted 38 home runs this season—spoke candidly about the “secret” to his home run production at ZOZO Marine Stadium, where strong sea winds blow, his thoughts on “Samurai Japan,” and the cheers from the fans.What is the true face of this “Japanese slugger” that Lotte fans have been eagerly awaiting?
From the November 6, 2026 issue of *FRIDAY*
PHOTO： Takehiko Kohiyama