Help on an Arc The Lad Fanfiction

I'm attempting to write a fanfction (or maybe two that just happen to intersect) after the events of Arc The Lad 3, involving Elc x Lieza and Alic x Marsia. Obviously, it's going to be romantic but I wanted there to be an overarching story about an important Guild mission that brings them (and a few other characters) together.

At the end of Arc the Lad 3 Alic and the crew end up sealing the Dark One in an arc and then everyone goes back to their regular lives. (Here is the youtube of the ending I know the characters put all their hands on top of eachother, then a bunch of sparkles happen with what looks like space afterward but it's never known what that the context of that was or what happened to the arc.

Ideas so far:
Alic, Elc, Shu, (being the top three trusted hunters) along with Marcia, and Gogen (Being the most famous and strongest magic users) are all summoned to the flagship Hunters Guild to decide what to do with the arc. The problem is, I'm not sure what to do with it myself. Also, if you think the arc is already gone then I'm going to need a new overarching plot(s) for these two couples to meet again and get together.

Any suggestions are welcomed.