Overlord, Vol. 4 (light novel) : The Lizardman Heroes

One day, in a peaceful lizardman village, an ominous messenger visits with a warning from the Great Tomb of Nazarick: In eight days' time, they will be annihilated. Unwilling to stand by and wait, the fighter and traveler Zaryusu journeys to the other lizardman tribes--who have received the same message--hoping to form an alliance against their impossibly strong opponent. But though the warriors try valiantly to resist, Ainz Ooal Gown and his undead army hold the power to determine their fate...