What does this side story have to do with the manga.....?

Hi! The manga is an anthology, which means it's a collection of stories :) the main story was chapters 1-4, 5 and 6 are standalones, and 7 is an extra for the main story, hope this helped ~

I really didn't know. I was so confused XD thank u~~

Nono it's fine it's my fault, I should've made that clearer in my chapter notes at the start and renamed the chapter to an extra :) Sorry!

Thanks for the update and letting us know! Can’t wait to see them again

Just want to say this is very common when manga gets printed into a book. It's not actually an anthology, they are just fillers since the main story didn't fill enough pages.

I've noticed it throws people off sometimes since people uploaded things differently. Sometimes they uploaded with the book, like you have done, and sometimes they will upload them as oneshots.
Though sometimes the manga was originally translated from the magazine so had no filler stories. Then someone gets the printed book and adds the unrelated stories later. (Even with longer, multi book series. The first one often has filler )
It's a whole mess of of organization and double uploads.
Just wanted to share what I've noticed.