Ok, after seeing all of the future chapter and fight predictions, I thought I would give it a try. This starts from the end of chapter 618. Don't be too rough in your criticisms, this is my first one. Also, it might be too "themed" for some peoples' tastes. Anyway, here goes:
New Fishman Pirates dive in to grab their captain after Zoro surfaces. Jones is unconscious, has a large wound, but is alive.
Zoro: Let's go!!
Neptune: This way, there is a part of the palace the water cannot get to, but we have to hurry!
Holding Brook while Zoro and Usopp swim quickly behind him, Neptune leads them to higher ground. All four climb some stairs and start running down a hallway.
- Foot steps are heard from behind them.*
Usopp: Guys, we got company!
Brook: Neptune-sama, do you know them?
Neptune: Their names are Dosun and Muhhi.
Everyone: (sarcastically) How'd you figure that out!?
Muhhi swings his spear and a slash flies towards them. They are still several hundred feet away, but it covers the distance rather quickly.
Usopp: (falls down) Aaaaah! It got me in the leg!
Neptune: He needs to be treated!
Zoro: Where's Chopper when you need him?
Neptune: Listen, a little further up, this hallway splits into a fork. I will go left, I can get him to the palace medical bay quickly from there. Brick, Zori...
Brook: It's Brook.
Zoro: It's Zoro.
Neptune (continues as if he wasn't cut off): You two go straight ahead, and try to draw them away from me and Usipp.
Usopp: It's Usopp.
Brook + Zoro: Got it
They arrive at the fork and go their separate ways. To the relief of Zoro and Brook, Dosun and Muhhi still follow them. They chase them through a few rooms at the end of the hallway before turning off to a side door.
Brook: Zoro, they just went in a completely different direction!
Zoro: I know just keep moving.
They enter a room with large double doors, Zoro notices a large plaque above the door that says "Synphonia Hall."
Dosun: So glad you could make it, Dosun!!
They hear the door bolt shut behind them.
Muhhi: If you want to leave, you will have to take the key from one of us, but we won't give it up that pleasantly, Muhhhiiiiii!
Zoro: Damn it, this is Enies Lobby all over again. At least I'm not cuffed to Usopp this time.
Brook: Alright, Zoro, we must fight these two.
Zoro: Yeah, I figured. Hey, where are we exactly?
Dosun: Dosun! We are on the floor of the good prince Manboshi's dance hall.
Zoro: Whatever, let's just get this over with.
Muhhi and Dosun both smile and simultaneously snap their fingers with all eight hands.
Zoro (draws his swords) Oni-giri!
Brook: Gavotte Bond Avant!
Muhhi and Dosun both dodge the attacks with a graceful ease, and both of their counterstrikes connect.
Zoro: Why did I take so long to react? Another instant and that would have hit me.
Brook: They are doing something Zoro-san, it's affecting our movements, but what?
Zoro: I don't care *He runs up up to Dosun* Nigiri Toro!
Dosun had enough time to get out of the way of the upward slash, sniggering all the while.
Zoro (thinking): Why did I pause right before my strike? Am I off my game today?
Muhhi: What's the matter, Pirate Hunter? Off your game today? Muhhiii!
Zoro: I wasn't off when I wasted your captain ten minutes ago.
Dosun and Muhhi look at each other again and smirk.
Dosun: Keep your eye on the hammer, Dosun!
Muhhi and Dosun move with almost blinding speed. Dosun reappears behind Zoro, and hits him squarely in the back with his hammer. Zoro is knocked far across the room but lands on his feet. Brook is blindsided by a swipe of Muhhi's spear.
Zoro: Are you guys rokushiki users, and what's with that footwork?
Dosun (smirks again): Good guess, but no, Dosun.
Zoro (thinking): Damn it, why can't we touch them, yet they can easily hit us?... Hold on, why are my ears ringing? My heart rate is lower too, much too low for a fight like this. *He looks up and notices a balcony above them, covered in black curtains.
Zoro: Brook! Attack one of them now!
Brook: Right! *runs towards Muhhi* Pirouette au Fer en Ronde!
As Zoro expected, Muhhi dodges with ease. Zoro watches as Muhhi begins to attack.
Zoro: Why did my heart rate go up just now!? Wait, that's it! Brook! Start singing, and make sure it's loud and off key!
Brook *Starts into a rendition of Binks' Sake*: Going to deliver Binks' Sakeeeeeeeee...
Zoro: Tatsu Maki no Arashi! (Lets out a piercing roar)
Zoro does a larger version of his Tatsu Maki. The move blankets the entire room before him (Brook is behind him), end to end, top to bottom. Muhhi and Dosun are both thrown to the opposite ends of the dance hall from one another and are quite dazed from the attack.
Zoro (Sheathing his swords): Well, that's one problem taken care of.
Brook: Zoro-san, that was amazing! Come on, let's go find Usopp and Neptune-sama.
Zoro: We're not quite done yet.
He removes the sheathed Shusui from his belt, and plants it forcefully into the floor with his left hand. The noise echoes throughout the room. A few seconds later, the balconies collapse. About a dozen fishmen and musical instruments fall to the floor on top of Muhhi and Dosun.
Zoro: Brook, the guy with the hammer still looks conscious, what say we pay him a visit?
They walk over to Dosun, and Zoro grabs him by the collar.
Zoro: Alright, talk. What's with the chamber orchestra hidden in the rafters?
Dosun: *chuckles* You were clever to figure out our ploy, Dosun. Since you beat us fair and square, I'll tell you. Since sound cannot travel that well under water, music has a different effect on fishmen than it does on humans, but not too different. With humans, when they move to music, their bodies move naturally to the melody, whether they know it or not, Dosun. With fishmen, our bodies only adjust to the tempo, not the melody, which is why we were able to move so fast (coughs). However, we had to play it loudly enough so that it would register with your subconscious, but softly enough so that you wouldn't hear it consciously...(Having trouble staying conscious while giving them the key) Bumblebees and anvils, Dosun (passes out with a grin).
Brook: That is very interesting. I never knew that about fishmen.
Zoro: What did he mean about bumblebees and anvils?
Brook: I have an idea, but first we must find Usopp and Neptune! I will tell you later, I promise. By the way, I'm going to start calling you Roronoa One Slice. I mean, the way you handled Jones then these guys was just incredible.
Zoro: Thanks. Sounds like a good plan. I just hope Neptune is willing to foot a bit more of the repair bill to cover the balconies. And just tell me what he meant.
Brook: Well, two pieces of music come to mind when I think of bumblebees and anvils. The first is Flight of the Bumblebee by the composer Korsikov. The second is the Anvil Chorus by Verdi-sama. The former is a very fast piece, very high tempo, while the latter has parts of its melody that are noticably slow. I'm guessing the fishmen played Flight of the Bumblebee when these guys attacked, and Anvil Chorus when we did, a very well timed procedure.
Zoro: Huh, music was never really my thing.
The two then leave the room in search of the king and their crewmate.