Antonio Inoki's Universal Fighting-Arts Organization alongside fellow judoka Naoya Ogawa. They were sent to New Japan Pro-Wrestling, where Murakami initially gained fame for attacking wrestlers while sporting a white mask, becoming known as "The Terrorist of Heisei". During his early career, Murakami split his time between NJPW and shoot-style promotion Battlarts to hone his skills as a wrestler. One of his first matches was at Wrestling World 2000, teaming with Ogawa in a losing effort to Shinya Hashimoto and Takashi Iizuka when he submitted to Iizuka. On April 7, Murakami took on Iizuka in an attempt to avenge his loss but he once again fell to Iizuka by submission. On May 5 at Wrestling Dontaku 2000, Murakami teamed with Ogawa to challenge Fighting Club G-Eggs (Yuji Nagata and Manabu Nakanishi) for the IWGP Tag Team Championship but lost when Murakami was pinned by Nagata. In early 2001, Murakami would also wrestle several times for the newborn Pro Wrestling ZERO1, main eventing the promotion's second ever show where he and Ogawa lost to Mitsuharu Misawa and Takeshi Rikio. Murakami became known for his wild, seemingly uncontrollable style of wrestling, predominately made up of punches, kicks, and legitimate judo/MMA throws and submissions, with very little actual wrestling moves in his moveset. In August 2001, Murakami entered the 2001 G1 Climax, his first time ever competing in the tournament. He finished fourth in his block with 5 points scoring victories over Nakanishi and Tadao Yasuda while going to a double countout with eventual winner, Yuji Nagata. In early 2002, Murakami joined NJPW full time, and in the summer, Murakami joined the heel stable Makai Club, where he was considered one of the highest ranking members behind only Tadao Yasuda. On December 10, 2002, Murakami challenged Yuji Nagata for the IWGP Heavyweight Championship. Despite making Nagata bleed and trapping him in his own finishing move, the Nagata Lock II, Murakami was defeated by Nagata. At Wrestling World 2003, Murakami and Yasuda lost to Michiyoshi Ohara and Shinsuke Nakamura. The following month, Murakami teamed with Yasuda in a #1 Contenders Tournament for the IWGP Tag Team Championship, making it to the finals before losing to Mike Barton and Jim Steele. However, an injury to Steele would give the title shot to Murakami and Yasuda who unsuccessfully challenged Cho-Ten on February 16. Throughout much of 2003, Murakami and the rest of the Makai Club feuded with