Only two-handed. Weapon mods specify that you can only use modified exotic weapons if you have the Modified Weapon Proficiency or Weapon Adept feats. Use a nodachi instead and call it good.
You do need to take weapon focus and ascetic style with a weapon you are proficient with and be 5th level. It should worth other than that one minor hiccup. Once it's part of the monk weapon group, ascetic style grants you proficiency as proficiency is effecting your unarmed strikes, and that covers the only complicated part of the feat interaction.
I see so I could do it with a nodachi then?
That would be nice as i would like reach
Nodachi doesn't have reach, you might be thinking of naginata. Is there a reason not to use one of the three monk reach weapons, Double-chained Kama, Kusarigama, or Kyoketsu shoge? If you're an unchained Monk, (if you aren't, why not?), you won't a non-reach weapon once you get Flying Kick anyway. Using a non-monk weapon wastes at least one feat, and is mechanically bad.
To use a non-monk weapon with Flurry of Blows without any multiclassing, you definitely need Exotic Weapon Proficiency, Weapon Focus, Ascetic Style, and Ascetic Form, and you need to apply the Versatile Design weapon modification.
The weapon modification rules don't exactly cover the "dual proficiency" weapons like katana. It could be rules in three different ways, from not working at all without either Weapon Adept or Modified Weapon Proficiency, to fully working even without either feat, but the by far most sensible interpretation is that you can wield the katana two-handed without either of those two feats, but need one of them to wield it one-handed.
For any other exotic weapon, you definitely need one of these feats, plus of course proficiency.
Once it's part of the monk weapon group, ascetic style grants you proficiency as proficiency is effecting your unarmed strikes, and that covers the only complicated part of the feat interaction.
What? Not only doesn't proficiency fall under "effects that augment an unarmed strike", and not only is there no proficiency with unarmed strike in the first place, but you need to select a weapon you're proficient with for Ascetic Style, and more importantly, for Ascetic Form.
Monk class features that now work with the weapon:
● Stunning Fist
● Ki Pool's DR penetration
● The scaling damage (works like Warpriest's Sacred Weapon)
● Dealing full strength on off hand attacks (almost never relevant).
Other things that now work with the weapon:
● Feats that enhance US, e.g. Possessed Hand
● Feats that have IUS as a prereq, e.g. Hex Strike
● Traits that enhance US, e.g. Bullied
● Spells that enhance US, e.g. Magic Fang
● Items that enhance US, e.g. Amulet of Mighty Fists (multiple enhancement bonuses don't stack, but other magic weapon abilities can be stacked with them)
Monk class features that do not work with Ascetic Style:
● The extra attack from Ki Pool
● Style Strikes
● Ki Blocker, One Touch, and Quivering Palm
● Flurry of Blows (relevant for tri-point double-edged sword, urumi, and the versatile design modification).
All of these are 'unlocked' by Ascetic Form, though.
Thing I'm not sure about:
● The ability to deal nonlethal damage without penalty (on one hand, that basically comes from the general rules for US, but on the other hand, it it explicitly mentioned in the Unarmed Strike class feature)
● Weapon Finesse
● Effects that only apply to natural attacks - the "is treated as (...) a natural weapon [blah]" line does make US better, but only indirectly.
@Scott: 'A weapon can normally only bear one modification at a time.'
@ AVR just so I Understand in the future
what all Feats would a Half-Elf - Unchained monk need (RAW)
To be able flurry and use his other monk features with his Versatile katana?)
Did you not read my post? I answered that question already. Do you not read posts in threads you start?
"To use a non-monk weapon with Flurry of Blows without any multiclassing, you definitely need Exotic Weapon Proficiency, Weapon Focus, Ascetic Style, and Ascetic Form, and you need to apply the Versatile Design weapon modification.
The weapon modification rules don't exactly cover the "dual proficiency" weapons like katana. It could be rules in three different ways, from not working at all without either Weapon Adept or Modified Weapon Proficiency, to fully working even without either feat, but the by far most sensible interpretation is that you can wield the katana two-handed without either of those two feats, but need one of them to wield it one-handed."
It depends on how you rual the "dual proficiency" issue. In any case, you need a feat for proficiency, because Weapon Focus demands that. The Ancestral Arms does cover that need.
How many feats you need depends on how you rule the "dual proficiency" thing. Katana's special quality and the weapon modifications have an interaction that is not covered by the rules.
Interpretation 1: Katana is an exotic weapon, and the weapon modifications rules say "An exotic weapon that receives modifications cannot be wielded without the Modified Weapon Proficiency or Weapon Adept feat.", with no exceptions for the katana's martial proficiency rule special option, as the weapon is still technically an exotic weapon. Under this interpretation, you need EWP and either Weapon Adept or Modified Weapon Proficiency.
Interpretation 2: Katana's special text says "Characters can use a katana two-handed as a martial weapon", and since weapon modification only affects the normal proficiency classification, this bypasses the increased proficiency rule. Under this interpretation, you only need Martial Weapon proficiency (but can't one-hand the katana).
Interpretation 3: Katana is classified as how you use it, which means you need EWP and Weapon Adept or Modified Weapon Proficiency to wield it in one hand, but only either EWP, or Martial Proficiency and either Weapon Adept or Modified Weapon Proficiency, to wield it two-handed. This is what I called the "by far most sensible interpretation".
Since you're the GM, it's your call, but I strongly suggest to go by the third interpretation. The result is that your NPC gets Exotic Weapon Proficiency (Modified Katana)* from Ancestral Arms, Weapon Focus (Katana) at 1st level, Ascetic Style (Katana) at 3rd level, and Ascetic Form (Katana) at 5th level. As addressed in the spoiler, Ascetic Style allows the character to use Stunnign Fist with the katana, and Ascetic Form allows the character to use Flurry of Blows, Style Strikes, and the bonus Ki attack with the katana.
*) That's actually necessary, and it does not grant proficiency with unmodified katanas.
Brawler is proficient with a non-exotic weapon with Versatile Design (Close), but a katana still has almost the same issues there as described above (only without needing EWP). Keeping with the sensible interpretation, the Brawler is proficient with and can flurry with a modified katana wielded in two hands.
That said, Brawler really wants a light weapon, because with a non-light weapon like a katana, Brawler's Flurry has a -4 penalty to all attack rolls instead of -2, and with no attack roll bonus, I'd say that's too much.
I'm not really sure what your goal is here. Is it for a PC or an NPC? If the latter, I think you're either overcomplicating the character building process, or you're creating a character that you shouldn't create (GMPC).
I could never figure out brawler's flurry. Can a brawler flurry with a two handed weapon that isn't a double weapon? It reads like they've only been given a modified two weapon fighting ability, but it doesn't discuss modifiers directly and the two handed line only mentions strength to damage not handedness. There isn't a two weapon fighting modifier for wielding a two handed weapon that I know of either. It was my impression that you needed something like spear dancing style to get a standard two hander to work with brawler's flurry.
Also, thanks Derklord for the corrections earlier, I thought I might have missed something. I could argue that unarmed proficiency does exist as it's granted to clerics with unarmed strike as their deity's favored weapon, but that's referencing another obvious error and doesn't move toward clarification at all. And it implies that unchained monks aren't proficient with unarmed strikes as it isn't listed for them.
I could never figure out brawler's flurry. Can a brawler flurry with a two handed weapon that isn't a double weapon? It reads like they've only been given a modified two weapon fighting ability, but it doesn't discuss modifiers directly and the two handed line only mentions strength to damage not handedness. There isn't a two weapon fighting modifier for wielding a two handed weapon that I know of either. It was my impression that you needed something like spear dancing style to get a standard two hander to work with brawler's flurry.
I'm with you - I have called Brawler's Flurry "one of the worst written abilities in all of Pathfinder", "one the most stupidly worded abilities in all of Pathfinder", and "abilities like these make me think that they must be written on drugs".
I've participated in multiple discussions about it, and here's the short version of how it works to my best knowledge and understanding: Basically, what Brawler's Flurry does, is a) grant the three TWF feats for free, b) allows you to use your main-hand weapon as an off-hand weapon as well, and c) hard-sets the strength bonus to damage rolls to 1x.
Penalties are still, as normal for TWF, determined by the weapon you use for your off-hand attacks (which is your only weapon): -2 if it's light, -4 otherwise.
Since you don't need to use a hand otherwise unused (or else it wouldn't work), the metaphorical hands FAQ should not be relevant for Brawler's Flurry. Meaning you can use a two-handed weapon (or a one-handed weapon in two hands), but you suffer the -4 penalty on attack rolls, and don't get a better strength bonus. You'd actually have different Power Attack ratios for the attacks (3:1 for main-hand attacks, 1:1.5 for off-hand attacks, yes you need to calculate and round down).
I was actually wrong about the unarmed strike proficiency. "All characters are proficient with unarmed strikes" CRB pg. 141
It's still not an effect but a general rule (important distinction), and thus Ascetic Style doesn't transfer it, and you still need to be proficient with the weapon befotre Ascetic Style can do something.
I could argue that unarmed proficiency does exist as it's granted to clerics with unarmed strike as their deity's favored weapon, but that's referencing another obvious error and doesn't move toward clarification at all.
Since proficiency with unarmed stikes is not enough to actually use them properly, those Clerics get Improved Unarmed Strike as a bonus feat. Warpriests have that baked into the class description.
Point of order Derklord: the PA bonus damage for offhand attacks is twice the PA penalty, not 1.5x. I think you've confused it with the way Str bonuses apply.
@Nosta: Derklord seems to generally know this subject better than me and I won't try to second-guess his judgement. My minor correction just now doesn't change that.
Point of order Derklord: the PA bonus damage for offhand attacks is twice the PA penalty, not 1.5x. I think you've confused it with the way Str bonuses apply.
Nope, in this case, it's actually 1:1.5, because we have to apply bo the +50% from "making an attack with a two-handed weapon", and the -50% from "making an attack with an off-hand weapon". Although you could argue that it simply cancels out (additive calculation) and isn't both applied multiplicatively, which would result in 2:1 ratio (rather than the normal 1:1 ratio for normal off-hand attacks).