6(TOTCF)

An Au where Cale ends up in Korea before he ever meets Choi Han and falls in love with Roksoo.

They live happily(well, as happily as they in an apocalyptic world) and had/adopted a few kids(how many is up to the writer) and taught them how to protect themselves but also have fun.

Everything was fine until during one mission Roksoo disappeared, leaving nothing behind so no one knew if he was alive or dead.

Maybe a year or more in the future, RokCale's kid discovers an ability to travel between worlds and accidentally ends up in TBOAH, in the Henituse territory.

There the kid is surprised and happy to find Roksoo, who later informs the kid that a god dragged him into that world to save and won't allow him to go back until he saves TBOAH world.

So you would think the kid would offer to help Roksoo or go back to tell Cale(and is possible siblings) that Roksoo was alive and fighting to return to them, right? But no, the kid goes back to Korea and grabs his family and brings them to where Roksoo is but now surrounded by a few allies(Henituse family, Molan duo, Choi Han, basically his first allies in canon) who are shocked to see Cale, who had disappeared, and the child(ren) that look a lot like Roksoo.

How they truly react, Cale's reaction to seeing Roksoo again plus his family, RokCale's kid meeting his non-human siblings, how the war would go, if RokCale's kid will kidnap anyone else to bring to TBOAH world, etc is up to the writer.