Arai was represented by Anore Inc., a talent agency founded in 1996 by actor Tadanobu Asano, Asano’s father Yukihisa Sato and Asano’s musician brother Kujun Sato. The talent agency terminated his contract shortly after his arrest on February 1, 2019.

Arai made his screen debut in Isao Yukisada’s Go in 2001 when he was 22 years old. His next film role was the emotionally disturbed senior high school student Aoki in Toshiaki Toyoda’s Blue Spring, which won him the Best New Actor award at the 17th Takasaki Film Festival.

Tokyograph announced in 2007 that Arai entered a “serious relationship” with singer Miu Sakamoto, the eldest daughter of noted musician Ryuichi Sakamoto and singer-songwriter Akiko Yano, after meeting during a television talk show in 2006.

In 2011, Arai co-starred as Detective Kazuhiko Soga in a one-off TV crime thriller Douki with co-stars Ryuhei Matsuda as Detective Ryota Udagawa and Chiaki Kuriyama as Michiru Soga.

The June 2012 issue of Switch, a Japanese arts and media magazine, features a special segment on top ten manga that teaches love and passion, chosen by Japanese actors, artists and musicians including Arai, who chose Bakuman while explaining: “You should up your girl power by learning how to behave like a heroine.”

On February 1, 2019, Arai was arrested for sexual assault of an outcall masseuse on July 1, 2018 by police in Japan. He was later indicted on February 21, 2019. On December 2, 2019, Arai was sentenced to five years in prison.