Nil no Koi Mahoujin
 

Nil, a 5th grader in an academy of magic falls in love with Kowloon, her scary-looking upperclassman. Will she be able to pluck up the courage to ask him to the academy’s dance party? She might need magic to give her a helping hand.


http://mangakakalot.com/chapter/nil_...ujin/chapter_1

Re: Nil no Koi Mahoujin
 

looks to be a one shot, though it would have probably have been a hilarious series if it would have continued. No process is involved, she simply goes from nerdy to sexy (not age progression). Nil is smaller than all the other girls her age and in order to gain the courage to ask Kowloon out, she uses magic to make herself sexy. That magic wears off in the end when she runs out of stamina and she reverts back poof style. It's a cute little one shot romance manga, not much substance to it, but tells a quick cute story.

The only reason I'm saying it's not age progression is a curious comment she made in one of the panels, I'm thinking there is some mistranslating going on here. Because she says, "Why am I so tiny, even though all the other girls my age look so grown up. My face has the freckled, nerd glasses look and I have almost no chest". So I'm wondering if the translator screwed her initial age up.