Rengoku Game

A mysterious event causes a number of people in Ikebukuro to collapse, but after they gain consciousness they explode and die! Ryuuji and his friend Taizou Miyauchi are determined to find the cause after their friend meets their explosive end in front of them. But instead of finding answers, they are given a death sentence and transported to a strange world by a mysterious child. To return home they must compete in, and survive, the Purgatory Games!

(Source: MangaHelpers)