Sesangman Guhago Euntoehagetseumnida

The only way out is through.
In the midst of a disastrous monster attack fated to end the world, a strange device throws Hee-Jae back in time 20 years where he meets the students of his foster father, Seok-Young. Now it's up to him to take them under his wing and stop the apocalypse so he can finally set off for a peaceful life.
(Source: Manta)