Another fic idea came to mind. So since So Mun didn't get the webtoon power up in the show, he'll get it while on his overseas trip. I'm thinking during one of his missions in the Season 3 webtoon where he got shot. That didn't stop the higher ups from extending his trip so he can activate the Counters powers worldwide. The team finds out about the injury of course and all want Mun to be sent back home but Yung doesn't want to until he completes his mission. Cue worried team, who almost starts a coup against Yung just to get Mun back. Yung finally relents only after Mun suffers another injury due to his non stop work which they conveniently forgot to tell the team. When he gets home, he's little worse for wear and that causes the team to be more angry. Mun doesn't want to make a fuss about it since he did agree to take on the job. They reluctantly let it go, temporarily at least so they can focus on nursing their youngest back to health. I'll include Ung-Min and Ju Yeon in there cause their Mom and Dad.
Another one is based on the others being busy to keep in touch with Mun.
Miss Chu has Jae-Youl.
Mo Tak is busy with police work.
For this fic, Hana starts seeing Do Hwi more.
Jeok-Bong, well, I'll think of something.
Jang-Mul, his grandparents and bestfriends are the ones that keeps in contact with Mun.
So maybe they, not intentionally, forget to like keep contact with Mun. He starts to feel that they no longer need him that much in the team since the others manage to take care of the evil spirits while he is away. He's happy that they have another life outside of being a Counter of course so he just talks to Jang Mul instead to get updates from home. When the trip was over he just goes back to Korea without telling the others.They only find out after Jang Mul tells them. Cue guilty team who tries to make it up to Mun but he doesn't see anything wrong with what happened which makes them feel more bad. I know it sounds so OOC of them but hey one can dream.