He is the head trainer of K-1 Gym Headquarters Team Pegasus and member of the K-1 Japan Group executive committee.
He won his quarterfinal bout against Fire Harada by unanimous decision on April 10, 2005, and advanced to the tournament semifinals, held on June 12, 2005, where he faced Hiroshi Iwakiri.
Kajiwara beat Iwakiri by unanimous decision and faced Takenori Hosono in the tournament finals, which were held on the same day.
[8] Kajiwara next faced Daisuke Watanabe at SURPRISING 8 MA Japan Kick on December 3, 2006.
[10] Kajiwara was booked to face Makoto Nishiyama for the vacant WFCA World Lightweight title at J-NETWORK "TEAM DRAGON QUEST 1" on June 3, 2007.
[14] Kajiwara was booked to face the former two-time WBC featherweight champion Chi In-jin at K-1 ASIA MAX 2008 IN SEOUL on February 24, 2008.
[15] Kajiwara suffered two consecutive losses for the first time in his career on May 31, 2008, as he lost a majority decision to Koji Yoshimoto at AJKF vs Team Dragon.
[16] Kajiwara snapped his two-fight losing streak with a third-round technical knockout of Kim Young-kwang at J-NETWORK TEAM DRAGON QUEST 2 on August 31, 2008, after which he was booked to face Haruaki Otsuki at K-1 World MAX 2008 World Championship Tournament Final on October 1, 2008.
[20] Kajiwara participated in the 2009 Krush lightweight Grand Prix, the first round of which was held on July 24, 2009.
[21] Kajiwara made his third K-1 appearance against Keiichi Samukawa at K-1 World Grand Prix 2009 Final on December 5, 2009.
He earned his place in the final two bouts of the tournament with a unanimous decision victory against TaCa on January 9, 2011.
[27] Kajiwara was booked to face Masaaki Noiri in the quarterfinals of the K-1 World MAX 2011 –63 kg Japan Tournament Final, held on June 25, 2011.
[28] After losing to Noiri in the first fight of the K-1 MAX, Kajiwara was scheduled to face Liu Wei in a non-title bout at Krush 12 on September 24, 2011.
[31] Kajiwara faced the 2008 K-1 Koshien tournament winner Hiroya in a non-title bout at Krush 18 on May 3, 2012.
He first dropped a unanimous decision, after an extra round was fought, to Yukihiro Komiya at the Road to GLORY JAPAN -65 kg SLAM event on March 10, 2013.
He won the fight by unanimous decision and announced his retirement from the sport in the post-fight ring speech.