When Atsushi Onita founded a brand new promotion, known as Frontier Martial-Arts Wrestling (FMW), he had a vision, a vision of company based around a more hardcore style of wrestling, of blood and glass and flesh meeting barbed wire.
Inspired by the death matches he'd participated in and witnessed during his time in Memphis, most noticeably the Tupelo Concession Stand Brawl (read about that HERE *insert link to Honky Tonk Man article*) he set out to change the face of wrestling as he saw it, or at the very least cut its ear off and set it on fire. He accomplished this mission.
FMW's insane, capital letters INSANE, levels of uncomfortable brutality set off a chain reaction and new deathmatch-oriented promotions like Wrestling International New Generations (W*ING), the International Wrestling Association of Japan (IWAJ) and Big Japan Wrestling (BJW), started cropping up even after FMW had folded after only 5 years.
Unlike in western wrestling where excessive violence had been used to escalate a pre-existing story, in Japan the death match style was simply creative violence for the sake of creative violence, blood for the sake of blood. In order to keep that level of spectacle interesting, constant demon-brained innovation was required, and the desperate need these promotions had to one-up themselves in terms of brutality created some match stipulations that were as insane, complicated and hard to watch as The Riddler's sextape.