Every jap rom-com(Or I guess I should call this a rom-camp...) needs a third wheel. It's mandated by the Japanes constitution.
I mean, it's not really a Japanese-only thing. If anything, it's generally better than most western romcoms of the last 40+ years:
Short ones usually start with one or both main characters already deeply romantically involved with their third/fourth wheel.
Long ones have a multitude of extra wheels, and one or both MCs spend the entire run sleeping with every regular or guest character they can get their hands on, while refusing to get involved with their actual romantic interest for the flimsiest of reasons despite obvious mutual attraction, until the very end (if at all, if there's a sudden axe).