There's no bigger stage in baseball than a World Series between the New York Yankees and the Los Angeles Dodgers, and there's no bigger star than Japanese slugger Shohei Ohtani.

The 30-year-old's ability to hit mammoth home runs, pitch over 100 mph and steal bases with ease got him a $700 million contract from the Dodgers this past offseason. But despite his on-field exploits, the 30-year-old is also known for being one of the most humble players in the league.

It's an approach that was instilled in him when he was just a promising high school athlete. Ohtani attended Hanamaki Higashi High School, where coach Hiroshi Sasaki designed the athletic program to shape his players as people in addition to as athletes, according to journalist Jeff Fletcher's 2022 book "Sho-Time".

For the players, who dormed at the school during the season, this included being assigned chores. The task of cleaning the bathroom always fell to the pitchers because of the outsized attention they receive compared to the rest of the team when they take the mound.

"The mound is the most elevated place on the field," Sasaki previously told the LA Times. "It's a stage. If you're on that stage, you receive the most attention. You get interviewed and written about the most."

Not wanting any of his pitchers to get a big head — especially a star like Ohtani, who as a teen was able to hit 99 miles per hour on the radar gun — the coach devised the chore as a way to keep them humble.

"Once they get up [on the mound], they are at the pinnacle," Sasaki told Fletcher for his book. "For the rest of the day I tell them, 'You have to do the lowest job.' Shohei never complained."

The task was also meant to teach players to take pride and care in their work, regardless of their role.

"If you see a toilet, you can see the value of a place, the purpose with which the people there approach their work," Sasaki told the Times, noting the care that Japanese department stores and hotels take in keeping their bathrooms clean. "It's the most important place in an establishment, just like the mound is the most important place on the field."

In the years since, Ohtani has remained humble. Even while earning tens of millions in the big leagues, the superstar has been known to pick up garbage when he sees it on the field.

And with tickets for the Yankees-Dodgers series climbing into the thousands, thanks in part to fans' clamoring to see Ohtani and Yankees superstar Aaron Judge battle for their first World Series ring, Ohtani hasn't been fazed by the bright lights.

"The goal was to get this far," he said after the Dodgers eliminated the New York Mets to advance to the World Series. "I also pictured getting this far with the contract that I've signed. I'm just glad we're at this stage."

Want to earn more money at work? Take CNBC's new online course How to Negotiate a Higher Salary. Expert instructors will teach you the skills you need to get a bigger paycheck, including how to prepare and build your confidence, what to do and say, and how to craft a counteroffer. Start today and use coupon code EARLYBIRD for an introductory discount of 50% off through November 26, 2024.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.