Chiba Lotte Marines outfielder Koki Yamaguchi made franchise history this past week, setting a new single-season home run record for a Japanese player since the team moved to Chiba in 1992. 

Yamaguchi broke the record on Friday against the Hokkaido Nippon-Ham Fighters at Es Con Field, launching his 26th home run of the season off star right-hander Koki Kitayama. The blast surpassed former Marines infielder Kiyoshi Hatsushiba, who hit 25 home runs in both 1995 and 1998. 

It came amid a particularly explosive stretch for Yamaguchi, who homered in four consecutive games from Aug. 26-29. 

He began the streak with a walk-off shot against the Fukuoka SoftBank Hawks on Wednesday, then hit his 25th the following day to tie Hatsushiba. After breaking the record with No. 26 on Friday, Yamaguchi added his 27th on Saturday against Fighters left-hander Kenta Uehara. 

The four-game streak was already his second of the season, having also homered in four straight games from May 20-24. Yamaguchi became the first Marines player to record multiple four-game home run streaks in the same season since Hall of Famer Hiromitsu Ochiai in 1985. The 26-year-old also finished August with 10 home runs. 

His new record applies specifically to Japanese-born Marines hitters since the franchise relocated from Kawasaki to Chiba in 1992. Several foreign players have surpassed the 30-homer mark during the Chiba era, led by Benny Agbayani, who hit 35 home runs in 2004. 

The full franchise record remains well above those totals as Ochiai hit a franchise-record 52 home runs for the Lotte Orions in 1985, when the team played its home games at Kawasaki Stadium. He batted .367 with 146 RBI that season to win the second of his three career Triple Crowns. Ochiai followed with another 50 home runs in 1986. 

However, no Japanese player for the franchise has reached 30 home runs in a season since Ochiai. Yamaguchi is now just three away. 

Among hitters with at least 300 plate appearances, he leads NPB in isolated power (.323), while striking out in roughly 22% of his plate appearances and walking around 6% of the time. 

The Osaka native was selected by the Marines in the fourth round of the 2018 NPB Draft. He debuted with the Marines in 2021 and established himself as a regular over the next several seasons, hitting nine dingers in 2021, 16 in 2022, and 14 in 2023. 

His production declined over the following two years before his breakout campaign in 2026. So far this season, he’s slashing .286/.335/.609 across 85 games with a max exit velocity of 113.6 mph, while his 31% pull-air rate ranks second in NPB behind only Shugo Maki. 

With a month remaining in the regular season, Yamaguchi has already established a new benchmark for Japanese Marines hitters in the Chiba era. His next milestone would be becoming the franchise’s first Japanese 30-home run man in 40 years.