Great Katana WS receive a MONSTOROUS boost to accuracy. There is no need to even think about ACC when using a GK weapon skill. They do miss, sure. But it's not enough for you to be concerned about. Don't sacrifice STR for accuracy during a GK weapon skill. Take a peek at my Samurai sets. They're not the pinnacle of the job, but they'll get the job done. Keep in mind I also have full Store TP merits, so I only need one piece of Hachiman along with Rajas/Brutal to maintain a 6-hit.
And people, STOP SUGGESTING ASKAR KORAZIN FOR SAMURAI TP PHASE. STOP IT. The only time you should even THINK about using that is if you're using Marinara Pizza +1, along with a full haste build in combination with Askar Korazin+Chivalrous Chain to maintain your 6-hit. Otherwise, it's TERRIBLE. You're losing out on not only the accuracy on Peacock Charm/Justice Torque, but you're also losing out on 16 accuracy from Haubergeon +1. (12 acc plus 4 from the DEX for us two-handers.) That can total up to -21 accuracy, which means about -10.5% hit rate. Do you really think you can sacrifice that without Marinara Pizza +1's accuracy? No. You can't afford it and be effective still. Gimp? Yes. You will be. And you'll be laughed at by every SAM who researched the numbers and know why it's crap. At very best, Askar Korazin is a WS piece for those who don't have Kirin's Osode.
And in regards to AF+1 hands, do NOT use them for GK weapon skill unless you can't afford Pallas' Bracelets. And with the price they've dropped to, there's no excuse to not have them at very minimum, Alkyoneus's if you got lucky or have the money.
Please trust me on this, I reasearched this job every step of the way while levelling it. I got advice from damn good Samurai across other servers, and suggestions contrary to what I've said are just going to get you laughed at by those better SAM's.
One quick edit... Don't merit Ikishoten. It's Shittyshoten if you gear properly. Just no damn excuse to have it. You other Samurai can't tell me there hasn't been a chance you've been waiting to start a fight, or been sitting on some extra TP just because you've already almost died once or twice on the mob. We're not talking about merit parties. We're talking about something that matters. If you're going to only merit on SAM, just don't level it. Say you're about to pop Tinnin, and you're one of a couple SAM's, and there's a couple WAR's, who came /THF to TA the tanks with weapon skills. Don't you think throwing them some extra TP when you can get 140-160 per meditate will help the rest of the alliance? It will help. Immensely. There's also situations where you're going to get your ***pushed in because you don't have another stunning job, and you're about to eat dirt. Oh hey, I've got Blade Bash. Bam! You just saved your own ***, along with the rest of the party like has been listed in this thread in regards to Nyzul Isle.
This job isn't cut and dry, but Ikishoten is NOT an option if you're playing the job right. Stop thinking support or nukers are at your beckon call, and are always going to stun to save your ***. Also stop being selfish, and help the rest of your alliance.