In 1998, Kasai made his debut in a Big Japan Pro Wrestling event in Osaka during the Deathmatch Wrestling boom of the late 90s. As BJW established a working relationship with American promotion Combat Zone Wrestling at the turn of the millennium, Kasai joined the stable "CZW Warriors" and feuded against the "BJW warriors". Kasai formed the stable "Big Dealz" in 2001, with John Zandig, Nick Mondo, Wifebeater, Z-Barr and Trent Acid. Since then Kasai has wrestled mainly for BJW and occasionally for other promotions such as Pro Wrestling Zero1, K-Dojo and Apache Pro-Wrestling Army. Kasai's body is covered in scars, from all the hardcore wrestling he has done. Including from a Fans Bring the Weapons Match from Combat Zone Wrestling show "Un F'n Believable", in which he took a bump onto a light tube board which ripped open his left elbow, exposing bone. In 2006 he won the first-ever IWA East Coast Masters of Pain after defeating Toby Klein, Mad Man Pondo and J. C. Bailey. Kasai has participated five times in an extremely bloody "Razor Deathmatch"; a hardcore match where boards are fitted with many razor blades. The first of these deathmatches was held in 2005 with Jaki Numazawa, in which Jun took a powerbomb onto the razor bladed board. In the second one, held in 2008, Kasai's match was against the American wrestler Masada. On November 20, 2009, he defeated Ryuji Ito in another razor match after a double underhook facebuster on a cactus. The fourth time was on April 5, 2010 Kasai competed in a Barbwire Treaty Death Match that pitted Team CZW against Team BJW in which a razor blade board was used in several bumps. On June 21, 2010 Kasai competed against the Necro Butcher in a Hardcore match for the Freedoms promotion; the razor blade board came into play mid way through the match. in 2009 In 2012, Kasai teamed regularly with American pro-wrestler/rapper One Man Kru. Together, they defeated the team of The Great Sasuke & Kesen Numajiro in a fluorescent light tubes death match at the September 9, 2012 Freedoms event in Iwate, Japan. He was born in Hokkaido and now lives in the mainland, but he is claiming that he is from "Hiladelhia, America" on his official website as a joke; he described Philadelphia as his second homeland. While Kasai wrestled in the US, he was a lodger in Wifebeater's house. He has described Wifebeater as a real mad man unlike many deathmatch wrestlers who are in fact gentlemen outside the ring.
