KUALA LUMPUR, April 1 ― In Ansel Elgort’s toughest role yet, the Hollywood actor learned Japanese until he was able to improvise his lines in one of the most difficult languages to master.

The teen idol spent four hours a day for four weeks to portray real-life American crime journalist Jake Adelstein in the anticipated HBO Max original series Tokyo Vice.

Adelstein is the first non-Japanese reporter at the Yomiuri Shimbun newspaper where he investigated the yakuza.

His 2009 memoir Tokyo Vice: An American Reporter on the Police Beat in Japan serves as the basis of the crime drama series.

Filmed in Tokyo, the show captures Adelstein’s daily descent into Japan’s neon-soaked underbelly in the late 1990s after he is taken under the wing of a veteran detective (Ken Watanabe) in the vice squad to explore the dark and dangerous world of the Japanese yakuza.

On top of learning Japanese, Elgort also studied journalism and the Japanese martial art aikido to master his character’s skill set.

He told Malay Mail yesterday it was the most prep he has done for a role which the 28-year-old described as fun but challenging.

The ‘West Side Story’ actor delivers most of his lines in Japanese in the crime drama. ― Picture courtesy of HBO GO

"We did a lot of prep working with Michael Mann,” Elgort said

"He likes to prep you to the point where things become second nature where you can really feel immersed in the role.”

The acclaimed crime auteur whose credits include Heat and Collateral, directed the pilot for Tokyo Vice and his vision set the tone for the series.

"I wanted to get to the point where I felt comfortable being able to improvise in Japanese because it’s freeing,” Elgort said.

"Initially when I was just learning the lines phonetically, you felt kind of like okay well, I can only say them one way now? Are we going to do one take or something? Where’s the range going to come from?”

For Elgort, it was necessary to know exactly what he was saying and how to say it in different ways.

"Those are challenging because the way you put stress on words in English is different in Japanese so it was clearly going to take a lot of work,” the Baby Driver actor said.

Elgort and Watanabe also served as executive producers for ‘Tokyo Vice’. ― Picture courtesy of HBO GO

Creator and Tony Award-winning playwright JT Rogers said it was amazing to watch Elgort’s commitment in learning the language ― most actors would learn foreign lines up to a certain point and fake it, but Elgort went all in and continues perfecting his Japanese until today.

"Not only did the audience have to be fooled, in a film sense, that this character spoke Japanese but Ansel got to the point where he does speak Japanese.

"Unique is an overused word in our profession but I think it is unique about our show,” Rogers said.

As Elgort grew more comfortable conversing in Japanese during filming, the actor who also executive produced the show would propose doing scenes in full Japanese and Rogers would say "let’s do it both ways”.

The separate Japanese and English scenes were often merged to reflect the actual way multi-lingual conversations happen.

"What if we create this fluidity where people who are bilingual just float back and forth without calling attention to it and that was really neat,” Rogers said.

"In Japan, sometimes you would notice that people would speak that way and you might call it Spanglish or I guess Japaneselish,” Elgort added.

The 28-year-old teen idol studied journalism and the Japanese martial art aikido for his role. ― Picture courtesy of HBO GO

"That freedom is something I wanted to have and I’m glad that I put the time in to be able to have that.”

Japanese actor Ken Watanabe who plays detective Hiroto Katagiri praised Elgort for immersing himself in his country’s language and culture.

As one of the show’s executive producers, The Last Samurai star oversaw the Japanese dialogues and did not hold back when it came to constructive feedback.

"[For some scenes], Ansel tried speaking Japanese but I couldn"t hear it and we tried going back to English.

"It was an honest relationship but he’s so hardworking,” the Academy Award nominee said.

Much like the mafia, the mysterious world of the yakuza may intrigue Western filmmakers but in Japan, it’s a topic many prefer to avoid.

When Adelstein wrote his memoir which was translated into Japanese, no publisher wanted to be associated with it because it stepped on too many toes.

Watanabe gave Elgort honest and constructive feedback on his Japanese lines. ― Picture courtesy of HBO GO

"I think it’s the first time we have a show about the real underground gangs, I think Japanese people are surprised and it’s interesting for them,” said Watanabe.

"I hope Japanese audiences will enjoy the show.”

The Memoirs of a Geisha actor added that there have been good films about outsiders setting foot in Japan such as Black Rain and Mr. Baseball but they didn’t offer an accurate depiction of city life in the East Asian nation.

"This series captures that reality and that’s because of Michael’s first direction.

"He wanted to show a Tokyo that was true and realistic.

"He had a consistent vision for the show from the art department to wardrobe and props, every department needed to deliver that realism,” said Watanabe.

Besides Elgort and Watanabe, the cast includes Academy Award nominee Rinko Kikuchi, Rachel Keller, Ella Rumpf, Hideaki Ito, Show Kasamatsu and Tomohisa Yamashita.

Tokyo Vice premieres the same day as the US with three episodes on Thursday, April 7 exclusively on HBO GO. Two episodes will debut every subsequent Thursday leading up to the finale on April 28.