I dont think a rival character is going to show up at this point. We've already seen Chokki getting jealous seeing him interact with girls from his grade. Plus there was that gyaru girl that almost joined but saw straight through Chokki and gracefully bowed out.I can feel it...
it's taking too long...
rival... I see it...
There was also occult club kidnfrom Chokki's grade .
The rival card has been played already and Chokki has fallen too hard for a male rival to be possible. Female rival is more plausible but Shun is already known as being with Chokki and, narratively speaking it doesnt serve a purpose. Just pointless drama