Hitokui

Multiple instances of mysterious mass deaths are erupting all over the city. The only similarity between each mass death is the time in which the victims were found dead. Trainee doctor Sasaki finds himself in the midst of one of these mass death events. He must now fight his way out of a dungeon ruled by a man-eating monster: "Hitokui." As other humans are slaughtered and eaten alive around him, will he be able to escape out of this dungeon and bring an end to these mass murders?

(Source: MangaHelpers)