This is so out-of-nowhere it's crazy, when I read this I thought I missed some chapter or something but nope, this is exactly after the talk in front of the convenience store, what the hell is the author thinking
"Oh hey, lets put some forced, out of nowhere character that JUST SO HAPPENS to work on the same convenience store that also JUST SO HAPPEN to be the previous owner of Sayu while he is JUST SO HAPPENS to be done with all of his seven girlfriend at the same time, oh and while at it, let's make it so that they JUST SO HAPPEN to never meet before even though the gyaru girl is basically Sayu's best friend now, yeah that will do"