
I can't help but thing that Jun will have a bigger part in the story later on or why would they even bother creating his character. I mean Ren entered his body after all.

Me, too. Plus they haven't explained the whole thing around Jun and Kou's births and Jun's mother's (Kou's aunt) death. NOR have they explained how the Nakanosawa Amano branch family was ejected from the main family in the first place. It's why Kamio's older brother was paired with that girl from the main branch family and why they looked down on Hazuki's choice, Jun.
Can't you do your revenge thing NOT FUCKING NOW?!