System mastery matters less than you might imagine. Really, I just need a sounding board.

I can understand that.  Creativity probably works best that way for most people; we're a social animal, after all.

Where did you want to start?

Actually that sounds familiar, now.  Apparently Sailor on the Seas of Fate is not so much a second book as a second collection of short stories.  Anyway, forget making it Stormbringer specifically, then... Just reduce it to an intelligent item that can empower and possibly control its wielder.  I've done things like that in homebrew RPGs (from before the first DF novel was published) making an evil version that dominated its user and a good one that could cause fiery wings, halo, etc. to appear on it's wielder.  Then there were the warforged from Eberron, which I liked.  I thought the idea of making a character from the perspective of the item could be interesting, but as already mentioned, others were recently thinking the same thing and it seemed to be shot down, though I hadn't seen the thread before it was linked here.
The 'Character Design Challenge' idea doesn't seem to be interesting many.  Maybe I've picked poor examples, or maybe it's something else, but it doesn't seem worth continuing at this point.

I've only 'read' the first two because they're all I could find on audiobook (vision issues).  Guess I was thinking of a less OMGWTFBBQ-epic version.  It's okay, the CDC thread I tried last week didn't exactly take off either.  I thought it would make a fun and interesting series of discussions, but if it doesn't work, oh well.

This is something of a game but also an exercise in creating game content.  The idea is to create a character, either one from a fairly well-known source outside of the 'Dresdenverse', or new one that doesn't appear in the books, but has a High Concept and description that fits.  Include names, aspects, skills, powers, etc. - everything that would be needed for someone to play the character or for a GM to 'borrow' and use as an NPC.  If you have an idea for a new Character Design Challenge, copy this introductory text and paste it into a new thread.

This time, let's try Stormbringer, the demonic black blade wielded by Elric, from Michael Moorcock's series.  The sword itself is a character, similar to the way a Denarian's coin is.  It could be handled with the Demonic Co-Pilot power, but what about looking at things from the sword's perspective?  If you can drink in the lives of those you kill and dole that power out until your wielder becomes dependent upon it, they'll eventually become dominated compel-bait.  If one wielder dies, no matter, any fool capable of lifting the blade can make a suitable replacement, in time... the sword itself is the villain.

Happy Hacking!
Thanatos

First, thank you for making this!  The skill calculation part alone is very helpful, especially when you have a skill-shuffling were-form.  Currently, I'm transferring the information over to the fillable PDF form for two reasons.

Using 2.0.3. Love it!
Only thing I have noticed is the Phases Worksheet. The Guest Star, and Guest Star Redux both print the information from Guest Star. Redux is not printed.

The first reason is similar to this issue.  When I look at the Phases Worksheet, it shows my Phase Four (Aspect, title, guest, story recap, everything) in both the Four and Five spots.  I don't know why it's doubled up like that, but I decided not to print it and just went back to the PDF for that page.

The second issue is much smaller, but it's why I decided to stick with the PDF for the main sheet as well.  I miss the pentacle graphic that normally shows up in the lower left.  I guess people could use that blank circle for their own symbol or a small character portrait, though.  Have you considered adding a way to import a character graphic to appear there?  The original pentacle could be there as a default, or someone could select a blank JPG to import if the really want the blank circle so they can hand-sketch something in.

Why not go all the way and make Dexter some sort of emissary/servant of the Erlking? It would definitely fit into the hunter theme.

Alternatively, you could play into the "dark passenger" as an actual entity, and give some sort of power involving sponsor debt with an agenda of pushing him to kill more and to drive him away from friends and family.  Nothing huge, a -1 or -2 cost maybe.

Actually, that's what the original author did with the character in the third novel, after which I stopped reading them.  I think the character works better as a psychologically damaged human than a case of demon possession.  You can wonder what it is about the human mind that breaks in that way, leaving it to develop without empathy, and you can consider just how far the average person is from becoming like that.  Saying, essentially, "um... it's magic!" is a rather unsatisfying non-answer.  The show isn't perfect, but it's the one case I can think of in which the show is more interesting than the books.
Still, if you prefer the demon-possession or hunter emissary ideas, more similar to the character in the books, write one up!  I'm trying to start these CDC threads as a way of collecting content for DFRPG games. 

He should work "You remind me of the man..." in as an aspect.  Everyone is going to be saying it anyway, whether it's the version by Atomic Fireballs or the Labyrinth one featuring David Bowie's codpiece.