A really cool thing happened recently as I was reading Joseph Campbell’s “The Masks of God: Volume IV Creative Mythologies”: A present day news item seemed to appear in one of the artistic pieces Joseph Campbell was discussing from yesteryear.
The present day thing of course was the Manic Pixie Dream Girl. The art from yesteryear that seemed to me to include some of that Dream Girl (at least according to Joseph Campbell’s descriptions, as I haven’t read these stories) was actually from two pieces by Thomas Mann: Buddenbrooks (1902) and “Tonio Kröger” (1903) and one piece from James Joyce: Portrait of the Artist as a Young Man (1916).
I was introduced to the Manic Pixie Dream Girl character by Anita Sarkeesian’s Tropes vs. Women video for Feminist Frequency. The term was originally coined to describe the character in films wherein a women serves to help a man on a life journey find his natural ability to be spontaneous and adventurous. In Nathin Rabin’s own words: “The Manic Pixie Dream Girl exists solely in the fevered imaginations of sensitive writer-directors to teach broodingly soulful young men to embrace life and its infinite mysteries and adventures.”
In Joseph Campbell’s “Creative Mythologies” he argues that starting in the 14th century in the time of the troubadours and their newly found independent and personal love, unsanctioned by the Church or the state, our central organizing principle has been the process of self-organization through “convictions derived from [our] own experience.” 
Before he references James Joyce and Thomas Mann, Campbell is explaining his enthralling idea that even in the present world of “sciences and machines” our young people are still facing an adventure and challenge within the mind. It is the “same adventure as thirteenth-century Gottfried: challenging hell.” I see it as trying to figure out “what to do in life,” while recognizing that work, or home or even family alone do not always suffice. It’s very much like the challenge faced by the “broodingly soulful young men” the Manic Pixie Dream Girl was conjured up to help.
He suggests that this adventure can be seen in many previous artistic narratives including Joyce’s and Mann’s:
Then again there is the coincidence (this time in two contemporaries) of James Joyce (1882-1941) and Thomas Mann (1875-1955), proceeding each along his own path, ignoring the other’s work, yet marking, in measured pace, the same stages, date by date; as follows:
First, in the Buddenbrooks (1902) and “Tonio Kröger” (1903) of Thomas Mann, Stephen Hero (1903) and Portrait of the Artist as a Young Man (1916) of James Joyce: accounts of the separation of a youth from the social nexus of his birth to strive to realize a personal destiny, the one moving from the Protestant side, the other from the Roman Catholic, yet each resolving his issue through a moment of inspired insight (the inspiring object, in each case, being the figure of a girl), and the definition, then of an aesthietic theory and decision. 
It was in this passage and specifically where italicized that I saw the Manic Pixie Dream Girl. So perhaps this character does not solely exist in the minds of modern day writer-directors but also at least existed as far back as over 100 years ago in the minds of famous authors like James Joyce and Thomas Mann. Thanks, Professor Campbell.
1) Campbell’s thesis is on page 65, the troubadours point is made on page 55
2) p 38-39