Wow, it's been a while... (^_^;) I was feeling nostalgic, so I read thru the manga over the weekend, and the fanart muse got hyper. A couple more things might be coming, but for now, I'll just leave this here!
One thing I noticed while re-reading the MTNN manga is how Yako calls Neuro "childlike" or "childish" in his views of the human world and how he approaches it - understandable, seeing as he's a daemon of Hell. And it's quite clear that Neuro is a massively powerful demon (if not the Demon Emperor himself
yes I like that fan theory
), so it's just accepted that he's also a mature demon, and most humans think he's a grown man as well.
But that got me thinking... what if Neuro came up from hell before
he grew up? What if he were the daemon equivalent of teenager, and his hunger overwhelmed any strictures Hell might have placed on him?
So yeah - teenage Neuro. He'd enroll in Yako's school, call her "senpai," and basically make her like a living hell 24 hours a day, because, while grown-up Neuro has the restraint to basically allow Yako to be at peace in school, I doubt very much a less mature Neuro would.