This is the conclusion, so enjoy, and once again, feedback is appreciated.
Fujitora gives a shout as he rears his head back, and the aura around it takes the shape of a dragon's head. An avatar of gravity surrounds him, pushing back everything nearby.
Jack: What is this power?
Fujitora races toward Jack, ripping his surroundings to shreds. Jack counters his strike with both swords, but Fujitora's entire body is now surrounded in gravity. Even Jack is unable to completely withstand it.
Fujitora: Time to end this game.
Concentrating his gravity aura in his sword, Fujitora lifts it above his head, ready to strike.
Before Fujitora can deal a final blow, Jack flips over him.
Jack: Mammoth Slam!
Right above Fujitora, Jack transforms into a full mammoth in midair. He falls toward Fujitora, instantly gaining momentum despite the gravity surrounding Fujitora.
Jack: I'll crush you!
However, Fujitora shows no sign of panic. Instead, he lowers his sword and lifts up his arm. The gravity aura surrounding his arm expands, and the dragon's claw heads up to Jack and grabs him. Jack convulses due to gravity pressing on him from all sides, and Fujitora tightens the arm's grip.
Fujitora: Even you could not beat the odds.
Fujitora swings his arm downward, and the gravity arm does the same, throwing Jack into the floor as the gravity speeds up his fall. Jack falls through several floors, until he finally reaches the bottom. Though he does not fall into the water, his impact destroys a large part of the hull, causing water to rush in. Jack reverts to his human form, bruised and bloodied all over but not down for the count. He leaps back up onto Fujitora's level, facing the Admiral once more. The ship begins tipping over moreso than it had before.
Jack: You're sinking your own ship. Do you intend to go down with me?
Fujitora: This ship was always doomed, but I have no intention of following you. Whipping Snake!
Fujitora spins his sword around, creating a spinning vortex of gravity aimed toward Jack. Weakened from his fall, Jack is caught by the gravity and is sent spinning through the ship's wall, out into the open. Fujitora leaps after him, and they fly out of the sinking ship toward the Mammoth. Flicking his sword, Fujitora sends Jack flying into the Mammoth's deck.
Fujitora: Sengoku! Did you evacuate the survivors?
Behind the Mammoth sail the surviving Marine ships. Sengoku and Tsuru stand on it as they move the injured Marines.
Sengoku: All of them! How's the battle?
Fujitora: Fine, but I require a bit of assistance. The thing we discussed before the fight.
Sengoku: Sigh...fine, then.
Meanwhile, Jack starts to pull himself up.
Jack: You bastards...
Jack is pinned down by Fujitora's gravity, but he barely notices it as he sees a giant, golden Sengoku flying toward him, fist at the ready. His momentum increased by Fujitora's gravity, he plants his giant golden fist into Jack, causing the Mammoth's deck to tear apart as the entire ship is nearly rent in two
Fujitora: Thank you, Sengoku-sama.
Sengoku: Eh, don't be so formal. You outrank me, so you get to finish the bastard off.
With Fujitora's assistance, Sengoku floats back toward the Marine ship. Fujitora has his back turned on the site of the impact, but senses Jack rising up.
Fujitora: Still up, after all that?
Jack struggles to bring himself to his feet, as he is cut, maimed, and bruised all over his body. His jaw mask is cracked, and his coat is in tatters.
Jack: I WILL...GET JOKER!
Jack transforms into his hybrid form as Fujitora lifts himself up on a piece of wreckage. Jack charges, intent on bringing down the Admiral once and for all.
Fujitora: We're done here.
As Jack picks up speed, the sinking Marine ship is lifted out of the water. But Jack does not see it. His only focus is on Fujitora, not his mission or anything else.
Fujitora: I'm glad I can't see this pitiful spectacle.
Floating upward on the wreckage, Fujitora sends the Marine ship flying toward the Mammoth. The clash rings loud across the sea, and both ships are decimated in this majestic spectacle. Fujitora then floats toward the Marine ship Sengoku and Tsuru are on. The debris from the collision clears, leaving nothing but flotsam.
Tsuru: Is he dead? That pirate was worth a billion berries...
Fujitora: I don't sense him anywhere nearby. He's a Devil Fruit user, so he's likely sunk.
Sengoku: I don't see any trace of him either. Well, he certainly lived up to his bounty! Did quite the number on you...we should get you to treatment.
Fujitora: I can wait...his onslaught left many in worse shape.
Marine Grunt: Admiral, Vice Admiral, Inspector General...both Vice Admirals Maynard and Bastille are in stable condition, as well as many other soldiers.
Tsuru: That's good news.
Fujitora: That bastard still killed many...I'd like to kill him all over again.
Marine Grunt: We're also drawing in closer to the Red Line...we should be at Impel Down by nightfall.
Sengoku: After this excursion ends, I'm going to eat food and play cards with Garp for a looong time. No more missions for me for a while!
Tsuru: We have to report to the Fleet Admiral when we head to Mariejois! Admiral...you should come with us and get your wounds checked.
Fujitora: Thank you, but I don't need to be tended to. Time for me to begin my trip...I'm going to look and see how far Doflamingo's empire really reaches. This Underworld business is honestly more frightening than any alliance. And if I run into Straw Hat or Trafalgar...well, maybe then I'll complete my original mission.
Meanwhile, back in the New World sea, a piece of flotsam had flown off into the distance after the two ships' collision. Lying precariously on it is Jack. He is a mess, barely alive and floating around in the middle of nowhere. But he is still breathing faintly and raggedly, ready to fight another day.