I say this every 3 chapters or so, but I need to say it again:
The "school" plotline of this manga is compelling, dramatic, and is way more than enough to carry this manga in terms of conflict, emotional stakes, and character development. This plotline alone would make this manga definitely one of the better mangas I've read.
The "evil psycho producer trying to create the ultimate band using murder" part has SOME potential but I feel overall detracts from the manga. I feel the author put it in to bring back Shiori's brother (Jouji?) and include more "27 Club" musicians, but right now I cringe every time I feel like the narrative is going to "waste pages" on that plotline instead of the really well crafted main plot. Maybe the author has plans for the "producer" plot to eventually take over as the main plot, and started with that vision, but I dunno.
Also, probably not related to the above, this manga is CRIMINALLY un-known.