The interpreter for baseball superstar Shohei Ohtani, Ippei Mizuhara, is set to appear in court Tuesday after pleading guilty to a single charge of bank fraud relating to allegedly stealing some $17 million from Mr. Ohtani.

The Department of Justice traces the scheme back to at least 2018, when Mr. Mizuhara accompanied Mr. Ohtani to a bank at Phoenix, where Mr. Ohtani opened an account to deposit his salary. At the bank, Mr. Mizuhara acted as an interpreter for Mr. Ohtani.

In 2021, Mr. Mizuhara began to place sports bets with an illegal bookmaker — bets that he lost and couldn’t pay off.

Using the information he had gathered while acting as an interpreter when Mr. Ohtani set up his bank account, Mr. Mizuhara logged into Mr. Ohtani’s account and registered a new email address and phone number that the bank would call to verify transfers.

This new email address and phone number were controlled by Mr. Mizuhara, not Mr. Ohtani, meaning the bank would call Mr. Mizuhara in order to verify transfers.

Between November 2021 and March 2024, Mr. Mizuhara used Mr. Ohtani’s bank account to pay his gambling debts — including one payment of $500,000 — and for other things, such as buying $325,000 in baseball cards from online resellers.

In one instance, Mr. Ohtani agreed to pay for $60,000 worth of dental work for Mr. Mizuhara. However, Mr. Mizuhara used Mr. Ohtani’s debit card to pay for the work without his knowledge. Mr. Ohtani then unwittingly reimbursed Mr. Mizuhara for the dental work from another account, transferring Mr. Mizuhara another $60,000.

“The extent of this defendant’s deception and theft is massive,” prosecutor Martin Estrada said in a statement. “He took advantage of his position of trust to take advantage of Mr. Ohtani and fuel a dangerous gambling habit.”

Mr. Mizuhara also allegedly engaged in impersonation of Mr. Ohtani to conceal his scheme and lied to others in Mr. Ohtani’s orbit to keep his theft under wraps. The scheme was discovered by the IRS.

“Our joint investigation with Homeland Security Investigations clearly showed Mr. Mizuhara not only stole from Mr. Ohtani, but also that he lied to the IRS about his income,” an IRS special agent, Tyler Hatcher, said in a statement. “Mr. Mizuhara exploited his relationship with Mr. Ohtani to bankroll his own irresponsibility.”

Mr. Mizuhara, though, maintains that Mr. Ohtani agreed to pay off his gambling debts ahead of time, initially telling ESPN, “Obviously, he [Ohtani] wasn’t happy about it and said he would help me out to make sure I never do this again.”

Mr. Mizuhara later walked back his claim that Mr. Ohtani agreed to pay off his debts, saying, “I’m ready to face all the consequences.”

In his plea agreement, Mr. Mizuhara admitted to filing a false federal income tax return in 2022, claiming to have made about $137,000 when in actuality he made some $4.1 million that year. 

In total, Mr. Mizuhara allegedly stole some $17 million through his scheme, a fraction of the 10-year, $700 million contract that Mr. Ohtani recently signed with the Dodgers.

In the initial indictment, Mr. Mizuhara was charged with both making a false statement to the IRS and defrauding the bank. Mr. Mizuhara has not technically submitted a guilty plea yet and is expected to do so at the arraignment Tuesday.