I believe it's just a manga (or light novel) thing, and nobody will be able to convince me otherwise. Naturally I reckon people there will start by calling each other by their last names, that seems to be the culture, but I won't believe the first name thing is anywhere near as big as manga makes it look like. Of course if people never get any closer to each other, they would never switch to first names.I can never understand the culture of first name. Like bruh, it's just a name. It's not even "baby" or "honey", I think those are more embarrassing than just the given name.
Japanese culture is super weird sometimes. Like, they'd be fucking and yet they'd still be too shy to call their gf bf by their names.