As the Gods Will(2011)

Deep down inside, high school student Shun Takahata craves for some excitement in his boring life…but his teacher’s head randomly exploding isn’t exactly what he had in mind. And when some of his classmates suddenly suffer the same fate, he begins to realize he’s been thrust into a series of deadly supernatural children’s games. Shun and fellow survivors are completely in the dark, not knowing who’s responsible, why it’s happening, or when it will end. To have any hope of unraveling the mystery behind the gruesome games, they’ll first have to outlast the games…and each other.

(Source: Kodansha USA)