Yuna is a cute but boyish succubus.
However since this is her first visit to the human world the sum of her sexual experience is zero.
To train and learn about sex, she chooses Masaya, the steadfast protagonist of this story.
She tries to seduce Masaya by showing off her virgin vagina, but then gets a taste of her own medicine as Masaya plunges her into a hell of continuous orgasms!

[From English DLSite]