They both deal with an MC who was previously involved with the military and is now trying to live a normal life as they deal with a traumatizing death in their past. They are then dragged back into fighting through meeting new people. Both shows also have awesome fight scene. But The fiery priest does have more humor then k2. Both are good shows.

both of these felt similar to me.
Similar humor and someone being in a situation that they aren't used to.
I also felt that the two actors were a little similar in their way of portraying the Main Character.

Both are really sweet Bl storys where one guy is insecure but the other guy makes him see that their love isn't wrong.