Being in heat may as well be the new default state of people in Hentai.
'Whenever she takes her glasses off', though...I'm sure some people might not appreciate how it only activates when it's taken off, but at least our protagonist does.
Not a bad deal though, it's almost like she has two different personalities separated via the glasses.
When I see a cute glasses girl I†˜m in heat too! But I†˜m a bit sad she takes them off to become a nympho... At the same time I think the guy is a hero for trying to have sex with her while she wears glasses... I†˜m conflicted... And horny...