Kaji is apart of the Watanabe Entertainment group named D-Boys. As a member of the D-Boys, Kaji also keeps a blog, which he updates occasionally and includes a personal video greeting from Kaji. Being a part of the D-Boys provided Kaji with a lot of opportunities. Among them was to perform with the group of boys and expand his experience as a performer. On August 6th, 2005, Kaji, along with Hiroki Suzuki, appeared on the radio program, Marvelous Radio Vibration that was hosted by fellow D-Boys members Yu Shirota and Yanagi Kotaroh. The D-Boys so far have released two Photobooks. The first photo-book released on April 27, 2005, was self-titled D-Boys, while the second, released on March 15th, 2006, was called Start, both which contain many photos of Kaji. From 2005 to 2006, he became the second actor to play Takeshi Momoshiro in The Prince of Tennis Musicals. Then on March 29th, 2006, in the Dream Live 3rd Live concert, he along with the majority of the Seigaku cast, graduated from their roles. Kaji was able to carry on his role as Momoshiro Takeshi from the musicals to the live-adaptation film of the anime/manga series, _"Tennis no oujisama" (2001)_. He, along with most of the principle cast members for the Seigaku Regulars, were able to reprise their roles in the movie. The film marked Kaji's first major film debut. The Tennis no oujisama (2006) was released on May 13th, 2006 and opened tenth in the Japanese Box Office. He has appeared in a various number of TV shows. On January 1st, 2006, Kaji, with fellow D-Boys member Hiroki Suzuki, appeared on the broadcast of Secret New Years' Performance Tournament "Young Man Colosseum", where Kaji displayed his acrobatic abilities. After his graduation from The Prince of Tennis Musicals, Kaji starred in the TV drama, Seishun Energy: Check It Out Yo! in Tokyo (Chekeraccho!! In Tokyo), which premiered on Fuji TV April 12th, 2006. The series was adapted from the movie Chiekeratsuchiyo, was 10 episodes long and featured Kaji as Shingo, one of the four main characters. The show was about four male high school students with no direction in their lives, until they found rap, which then inspired them to take charge of their lives and their dreams. He, along with his three costars (Masataka Kubota, Ryo Kimura, and Gota Watabe) formed ROM-4 for the show and released a CD single called "Keep It Goin' On" for the show as well. Next, he would appear as a member of The Tigers, in the TV drama, The Hit Parade, starring fellow D-Boys members Masato Wada, Yuu Shirota, Hiroki Suzuki, Hirofumi Araki, Yuuya Endo and Seto Kouji. The show aired May 26th, 2006 on Fuji TV. Kaji's currently appearing in the TV drama, Regatta, which is airing on TV Asahi. The show's about a university rowing club, in which Kaji has the role of playing the freshman, Toshiyuki Hoshino, on the team.