Yuichiro "Jienotsu" Nagashima (長島☆自演乙☆雄一郎, Nagashima Jien'otsu Yūichirō; born July 2, 1984) is a Japanese cosplayer, retired kickboxer, mixed martial artist, known for his career in K-1.

Yuichiro Nagashima was born in 1984 in the city of Nishinomiya, Hyogo. He started learning Judo when he was an elementary school. He continued training Judo until the graduation of Middle School. During his High School life, he practiced Karate, but he attended training only once or twice a week. He first intended to become a Professional Wrestler, but was deemed too short, so he decided to be a fighter instead.

Nagashima joined the team of Nippon Kempo and started training seriously when he was matriculated in University of Marketing and Distribution Sciences. In addition, Nagashima started participating professional mixed martial arts bouts. He also started cosplaying anime characters during his entrance to the ring.

In 2007, Nagashima shifted his focus to kickboxing and has gone on to become known as the "Otaku Kickboxer" due to his love of anime and cosplay entrances before bouts. He won ten consecutive victories to start his career, fighting for Deep, Mars and New Japan Kickboxing Federation. On November 9, 2008, he defeated Teruaki Furukawa for the vacant NJKF Super welterweight title; this marked the first time a kickboxer from a non-NJKF affiliated gym had won an NJKF title. On January 25, 2009, he was chosen and awarded 2008 Outstanding Performance Award by NJKF, and also given 3 more awards certified combat sports medias.

After winning the title, Nagashima was offered by K-1. He participated K-1 World MAX 2009 Japan Tournament on February 23, 2009, and he knocked out Hayato at 2R at the quarterfinal, but he was beaten by Yuya Yamamoto and lost by TKO because of being cut at the semifinal.

After the Japanese tournament, Nagashima was offered to fight against Albert Kraus from Netherlands on April 21. They engaged in a heated war of words before the bout where Kraus said "he seems to be a gay", while Nagashima demanded Kraus to cosplay Yoko Littner from Gurren Lagann if he lost the bout. The fight ended in Nagashima losing by knockout in round one. On October 26, Nagashima was offered to fight against Xu Yan from China. Although he trained at Masato's gym, he was knocked out at round one. In December, he was awarded the 2009 Walkout of the Year by Inside MMA of HDNet.

On March 27, 2010, Nagashima participated to K-1 World Max 2010 Japan tournament. He won the tournament with 3 consecutive knock outs. Although he wanted to defend his NJKF title after this tournament, he returned his title as on 1 April because he was going to participate the world tournament and it was hard to arrange his schedule for defending title.

On December 31, 2010, Nagashima took part in a "mixed rules" bout against Judo and Brazilian Jiu-Jitsu expert Shinya Aoki at Dynamite!! 2010, the annual New Year's Eve fight festival. One round was to be held under Kickboxing rules and the other under Mixed Martial Arts rules. A Coin Toss decided that the Kickboxing round was to commence first. Aoki took advantage of the fact that he only had to survive through a single three-minute round of Kickboxing and thus threw pointless attacks like flying dropkicks and rolling heel kicks while holding onto the ring ropes in order to run the clock down. As the second round began, and Aoki now in his element under MMA rules, he dropped immediately for a Double Leg Takedown, while Nagashima launched a Flying Knee square into Aoki's jaw. The blow instantly knocked out Aoki, after which Nagashima followed up with a number of hammerfists on the supine Aoki. The referee stepped in and stopped the fight four seconds into the period.