So, I basically did this in an attempt to optimise Fighting Defensively hardcore. This uses the Weapon Group variant from UA, the assumption that Spinning Swords fall under Exotic Weapons (Flails and Chains), and that Swashbucklers get Basic + 3 Weapon Groups - this is the only real big leap, and seems reasonable enough to convince a DM.
If not, I guess you've got to find another way to get proficiency in Spinning Swords.
Dodgy McDodgerson
Build Stub: Kalashtar Swashbuckler 1/Hit-and-Run Fighter 2/Swashbuckler +2/Dervish 3/Duelist 5/Dervish +4/Duelist +3.
Substitution Levels: Darksong Knight 2 (Fighter substitution level, requires patron deity Elistraee and Knowledge (Religion) 1).
Skill Prereqs: Knowledge (Religion) 1 and Perform (Dance) 5 by 3rd level. Tumble 5 and Perform (Dance) 8 by 6th level. Everything else? Negotiable.
Ability Scores: Str, Dex, and Int 13, minimum. Otherwise, pump Int and Dex.
Feats:
1st Level: Dodge, MobilityFlaw, Weapon Focus (Spinning Sword)Flaw, Weapon FinesseB. Flaws are Shaky and Vulnerable.
2nd Level: Combat ExpertiseB
3rd Level: Path of Shadows, Power AttackB
6th Level: Dancing with Shadows
8th Level: Spring AttackB
9th Level: War Devotion
12th Level: Elusive Target
15th Level: Deceptive Dodge
18th Level: War Devotion
The Cool Bits
This is a very late bloomer, but bloom it does.
At 20th level, start Fighting Defensively. Sure, you take a -4 to your attack rolls, but you get a +2 bonus to AC!
Increased to +3 by 5 ranks in Tumble. Then to +7 by Elaborate Parry (Dervish 7). Then to +15 by Elaborate Parry (Duelist 7). Yeah, they have the same name, but they are completely different class features. Also, use Graceful Lunge (Dancing with Shadows). You'll see why.
Next round, you get +15 to your first attack due to Graceful Lunge (adds your AC bonus from Fighting Defensively or Combat Expertise to your first attack roll the next round).
War Devotion makes this more interesting; by 20th level, it turns your Fighting Defensively from -4/+3 to -1/+5. This turns Fighting Defensively into a +17 to AC and +17 to the first attack you make the next round, in exchange for a -1 penalty to attack rolls on the first turn. You can do this twice per day.
Also, tag the big boss monster you're fighting with Dodge; I hope they weren't relying on Power Attack for damage (Elusive Target renders you immune), that they weren't Flanking you (you automagically redirect the first melee attack they make that round to the flanker if that's the case), and that no-one tankier is standing next to you (Deceptive Dodge turns one miss each round into an attack made against a creature adjacent to you. Technically, there is nothing to stop you from redirecting their attack back into their own face.)
The Problems:
None of the stuff that makes Fighting Defensively worth it comes online in early levels (both versions of Elaborate Parry come into play at 7th level of the respective classes), and War Devotion only lasts one round (unlike other Devotion feats, that tend to last one minute).
If you want to fix these problems (and why wouldn't you?), I suggest letting War Devotion last one minute in exchange for a Swift action activation. Also, roll the Duelist's Elaborate Parry into Canny Defense - it can do with the buff, and getting improving the bonus from Fighting Defensively by your class level is great to have from 1st level instead of 7th.
