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

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.

I AM SO ANGRY WHAT THE FUCK IS THIS? THAT SEME NEEDS TO PUT SOME GOOD SENSE INTO THAT HEAD. AND THAT UKE NEEDS TO REALLY PULL SOME RESISTANCE. That seme is fucking around and claiming the uke as his at the same time. And that uke just doesn't complain to much. LIKE PLEASE PUNCH HIM AND GO FIND YOURSELF A GOOD MAN
For me it's the uncensored PPs