Purity as a character trait is a very common concept in fiction. Going back to some of the earliest mythology, purity is treated as an ideal goal for everybody to strive towards. Purity is usually defined as a total lack of sin with an unrivaled dedication towards the ideals of the culture. In this sense, outside ofdeconstructions, purity is almost always analogous to goodness. It is often analogous to virginity as well, but not entirely bound to it. This can often go to supernatural lengths.
Going more in depth, a character with this trait (usually female, but male examples aren't that uncommon) is treated both by the narrative and by many (if not all) of the characters as being a shining example of good. Almost alwaysbeautiful, she often gives off a soft radiance that tends toattract animals. Almost exclusively soft-spoken, polite, optimistic, and just all-around pleasant to be around. The general message tends to be that this is a near-angelic person and should be given the utmost respect.
Probably one of the first tropes to be consumed by the overly-inclusiveMary Sue label to such a point where any character like this will be immediately labeled as one regardless of context. Because of that, it isn't quite so common any more but is still a decently popular template in some circles.
Sailor Moon dedicated its third season to aMacGuffin hunt involving "Pure Hearts", a crystalline object residing within people with a pure and just dedication towards a goal. Not played entirely straight in the fact that even bitter, cynical characters have them as well.
Penelope fromThe Odyssey. She was never tempted by her suitors and worked hard to outwit them so they'd leave her alone. She also spent most of her time in mourning. Slightly to be expected since she's the image of an ideal Greek woman.
Warhammer 40,000 hasSanguinius, Primarch of the Blood Angels, complete with golden armour, gargantuan silver-white wings, badassPapa Wolf trait andHeroic Sacrifice without ever swaying from his path, all the while being beloved by all for his nobility and generosity, which became something of his nickname; the 'All-Beloved'.
Kairi, and the other six Princesses of Heart inKingdom Hearts.
Also Ventus, since Master Xehanort took away the darkness from his heart.
Subverted with Sera fromDigital Devil Saga. She fits the criteria of being aMystical Waif, aMacGuffin Girl andThe Ingenue - mostly becauseshe can talk to God. But this turns out to bite her in the ass: she was partially responsible for God absorbing the Earth's data; createdA Is of people she knew (which were eventually used in a survival-of-the-fittest experiment to create powerful warriors) and was generally manipulated by her own mother, Serph and a lot of the other scientists. She alsotakes a level in badassery in the second game.
As mentioned above, very popular in classic Disney movies. Later princesses (Ariel,Belle,Jasmine) were notable for going against their cultural norm (this was, obviously, post-feminism), but the originals were played straight.