MC was sleeping in some tomb/coffin down underground? Humanity is facing another race that wants to enslave them. (Some elvish looking race?) MC gets woken up by a team of explorers so he (I think they mistook him with another person) can save humanity or something. It was written in a particular way, every 3 chapter would be (1: Present time, 2: POV of another person, 3: MC's past). I don't really remember much more other than this. If I recall correctly, the MC wasn't the person they were looking for but MC taught them some magic to defend themselves?