I would like this to be serialized, but then it's probably get ruined with another lame love interest so it's probably for the better than it's a one shot
Idk how you're going to serialize this? Like the whole setup is created for a one time joke.
Surprise, she's actually your osananajimi who stopped developing mentally from 4th grade
Whoopsie the entire family being fed upon that as a misunderstanding.
And then what? Author prolly gonna be forced to dip into your usual second girl joining along with lame drama. The way I see it, the only serialization is in the form of web comics with usual ≤5 pages each chapter.
The girl is mischievous but childish and dense. She'll keep getting 'naughty' ideas that'll confuse and worry MC until it turns out it was a bunch of silly horseplay instead.
I mean, that kinda setup reminds me of this, also just a little bit of this, and maybe this even though it's not similar at all.