Jirisan (2021)

Nature is wild, man is wilder.

Both series involve rangers/police officers fighting off dangerous people in remote parts of natural parks / the border.

The stories are gritty, there are a lot of subtle details that you have to pay attention to, the cinematography is superb, the cast and crew definitely know what they're doing.

Recommended!

The chemistry between Lee Je Hoon and Kim Hye Soo feels similar to Joo Ji Hoon and Jun Ji Hyun, the female sunbae teaching the newbie and working together as a team. There's also mystery in the plot and we have different cases in every episode.

Both dramas are related to saving lives in tough nature conditions and tell about rescue activities.

Both dramas deal with first responders or rescuers. There's a mystery in each, and all the people in the main cast have interesting back stories.

Both dramas also involve episodic cases and an overreaching arc, and the MCs bond over their problems and how they deal with them.

Jirisan happens in nature and in Missing it's similar.
These two also have the fantasy/mystery element that really takes a strong part of the story.
There are moments of teamwork for both shows though for different purposes.
In Jirisan, they are looking for people who go missing on the mountain while Missing is sort of a different perspective of searching for those who go missing.

Both series are very much a mixture of folklore, folktale, legends, and myth. This aspect differentiates two series from others tagged with a combo of [Mystery, Thriller, Drama, and Fantasy].