I just thought I would relate a quick anecdote from my last solo game where I was actually playing a fallen in the new World of Darkness world and while playing through an adventure (from Cthulhu Britannica, no less) I found myself helping a true fae to clear out an evil wizard who had sacrificed thirteen people to build up wards to dominate her brother and drive her out of the location.
While the adventure was complicated when I immediately fell down one of the first pits in my attempts to smear the chalk outline (amazing how Cthulhu adventures can merge with World of Darkness), I managed to return to him and fulfil the quest.
So what does my dear new true fae pal do? She asks me what I should like as a prize. I ask to leave, having wizened up to their inhuman natures, but she refuses as she doesn't feel that would be reward enough.
Since I had previously reassured my human friend (and one-time thrall) that he won't always be so weak once I arm him to the teeth with magical weaponry (which fallen can do if they have the right lores), and having joked about getting him a flaming sword, I asked for such an item. He was complaining about feeling ineffective and I had been needing to leave him behind while I go off and adventure, after all.
She grins and takes me through a portal to her world where she points out a sword embedded in a big stone. I try to draw it, fail, and she hints that it may not be for me. So I let my human buddy, Henry, grasp it and draw it. Arcadia ... True Fae ... a mortal ... my demonic PC knew little about these factors.
Anyway he rolls up his sleeves and gets to it, straining to remove the blade. As it slowly gets pulled loose, the rock begins to crack and lava seeps out of those cracks, splashing on his feet and then writhing up his body in tendrils, plunging below the skin and seeking out his heart. Set alight as a human touch, he screams, and so I use my revelatory form's "Immune to Fire" ability (not that it helps against supernatural sources) and try to pull him loose.
Finally it ends, leaving him obviously traumatised and with ribbons of glowing fire beneath the skin and the occasional heat spark dancing through his hair and a glowing flame in his heart. He pulls the sword finally loose and stands there gasping.
The true fae then provides me my flaming sword, in the shape of my human friend, and says I will have him for a year and a day and that if he does not serve me admirably as my sword then he will return to her at the end of that time.
This is with that Shaitan character I've described earlier that I've played in numerous realities and universes (much like a beloved comic book character) because I'm lame like that. Currently she's an anthropologist in the modern world (as we grew tired of that apocalyptic landscape previously described).
So having been resculpted into a living weapon herself in the time of the Fall, she's particularly sensitive to having essentially done the same to her friend through a foolish slip of the tongue.
Anywho, intense and a nasty surprise for any of your players should you be running Changeling. The fae are dangerous to both cross and to help.
ADDENDUM: Conversations in the comments section reveals that a number of other players wouldn't be as cool with this as I am. Thus I will add in a few details of what made this work in case you're thinking of trying this at home: Know Your Players (I mentioned this possibility with a smile; I spend much of my spare time daydreaming about worst case scenarios; I love deep and intense plot developments), Check With Your Players (I mentioned evil sword and he grinned before asking me if he should do it to which I responded that he might as well), A Prize For Every Cost (He will be far more useful now rather than being constantly sidelined and now he has a fancy sword), Style of Game (You can generally get away with more intense plot points in a solo game where you have adequate time to explore the ramifications and where you require more in-depth NPC characterisations).