This webtoon is a brand webtoon of Ragnarok Arena.
Ran and Maruna have fallen into the world of Ragnarok Arena!
Their special monster collection begins!

From BaboKimScans:
This is a spin-off of "One Last God Kubera" by the same author. KubeRag Arena is a promotion for the mobile game "Ragnarok Arena" that recently released in Korea.
Two of the original story's characters find themselves on a strange planet amidst their travels. They are given the mission to calm berserking Monsters to find a way back to their original world.