Sitting in the third-floor lounge of a hotel in Cambridge, Massachusetts, Masanori “Mashi” Murakami leaned forward in his chair and hummed the melody to the Sukiyaki song.

He was relaxed. Not like 51 years ago, on September 1 1964, when he began humming the famous Kyu Sakamoto song as he came out of the Shea Stadium bullpen in the eighth inning, with nearly 40,000 fans watching.

“I go to the fence and the door opens, and I go in,” Murakami recalled. “I’m walking to the mound, that time, wow. But [being] inside [the field] is very different. Maybe if I get nervous, it’s not good. Now, I think OK, make me relax. The stands, the people. I can hear, but I don’t know what they’re saying. I understood a little English.”

Mashi began to ease up as he hummed the Sukiyaki song to himself on his way to the mound, then pitched an inning of relief and struck out two batters.

What 20-year-old Mashi didn’t realize then was the gravity of the situation, as he had just became the first Japanese player in Major League Baseball history.

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Mashi pitched to a 5-1 record with a 3.43 earned-run average and 100 strikeouts in 54 games with the Giants over parts of the 1964 and 1965 seasons before returning to Japan to honor his contract with the Nankai Hawks.

On Monday, Mashi, 71, visited Fenway Park to share his story at an event hosted by the Japan Society of Boston, alongside Robert Fitts, author of the biography, Mashi: The Unfulfilled Baseball Dreams of Masanori Murakami, the First Japanese Major Leaguer, and Yuriko Gamo Romer, director of the documentary Diamond Diplomacy.

“I was never thinking of the major leagues,” Mashi said before the event. “I just wanted to pitch.”

Mashi surprisingly pitched with great success, but his only regret is that he didn’t pitch longer in the United States.

The start of his 1965 season was delayed, as the Giants and the Hawks worked over a contract dispute. Mashi was ultimately allowed to play with the Giants, only if he honored the promise he would return to the Hawks after the season.

Once he did, another Japanese player did not play in the MLB for 30 years until Hideo Nomo debuted for the Dodgers in 1995.

As Fitts writes in his book: “The dispute over Murakami’s contract would ignite an international incident that ultimately prevented other Japanese players from joining the Majors for 30 years.”

But for the short time he pitched in the Majors, Mashi was making a profound impact, even if he didn’t know it yet.

“I wasn’t thinking about all of that other stuff. And I was stupid,” Mashi joked.

“When I went to the mound, I was never scared. I didn’t think about who was coming up at bat. Who is Hank Aaron? Who is Pete Rose? Who is [Roberto] Clemente? I didn’t know. I didn’t care. I pitched my same style as in the minor leagues.”

After Mashi signed as a 19-year-old with the Nankai Hawks of the Japanese Pacific League, they sent him to the United States to hone his skills.

San Francisco Giants’ Japanese pitcher Masanori Murakami is seen in this 1964 photo. Photograph: AP

He arrived at Giants spring training with an English dictionary in one hand and a Japanese dictionary in the other, the only way he could communicate with new teammates like Willie Mays, Gaylord Perry and Juan Marichal.

“It was good for me because I learned fast,” Mashi said. “With an interpreter, [you learn] nothing.”

Mashi began the season in Fresno, where he pitched to an 11-7 record in 106 innings, with 159 strikeouts and a 1.78 ERA.

He played his last game in Fresno August 29, before Fresno manager Bill Werle told him he was promoted to the San Francisco Giants.

The Giants sent him to New York with a one-way ticket, a daunting trip for somebody in a foreign land.

After he arrived at JFK airport, Mashi went to the Roosevelt hotel and headed to the concierge desk to check in, only to find out his name wasn’t on file. Mashi asked the concierge to check again, but still there was no name.

He grabbed his bags and sat in the corner, wondering if he would ever join his San Francisco Giants teammates.

“I’m thinking: if nobody comes, what do I do?” Mashi said. “Maybe tomorrow morning somebody might find me in the Hudson river.”

Of course, the Giants eventually came for Mashi. When he got to Shea Stadium and practiced before his debut, Giants GM Chub Feeney had Mashi sign a contract – although he couldn’t understand what exactly was written on it.

What he did understand is that if he didn’t sign it, he couldn’t play.

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There’s a watershed moment of sorts for Mashi and his impact on the Japanese American culture when he played in the United States. During a game against the Dodgers, Mashi tried voicing his displeasure with the home plate umpire after a call he didn’t agree with.

The only problem was Mashi couldn’t argue because he didn’t understand enough English. Instead, he angrily tossed the Rosin bag in the air before he threw his next pitch.

Later in San Francisco, a man came up to Mashi in a restaurant and thanked him after watching the game on television.

“He said by doing that one little action, in some ways for this generation of Japanese Americans, it relieved many years of upset and oppression,” Mashi explained with the help of Gamo, who translated.

“I don’t know name, but he was emboldened by this action.”

Even then, Mashi didn’t fully understand the impact he was having.

As he sat at the hotel Monday, Mashi reflected on his career and the passageway he opened for future Japanese major leaguers, even if it was cut short.

“He has some understanding [now] that there was a purpose, that it had some impact,” Mashi explained via Gamo’s translation. “But he has some concern it caused some trouble.”

“Every player that can come over here and play baseball, I think is very good,” Mashi said. “Each man only has one time at life…to reach the [highest level] of baseball.”