Hexadecimal Murder

Kenji Satou is a 21 year old prosecutor. When he and 15 other people are kidnapped and taken to a mysterious place, they are told by Kitsune, a large talking fox, that if they want to escape this place, they must commit murder.
The idea isn't as simple as killing someone, though. Every 3 days, they will have an "arena game" where they must find a belt, and whoever wants to escape must find it and then put it on someone. The person who has the belt around them will be put through a grueling execution, and the person who put the belt on them will get to escape.
However, Kenji soon discovers that larger forces are at play here, and that maybe Kitsune isn't the one behind this...