Shiki was a notorious pirate during the age of Gol D. Roger (called Gold Roger by most people) who wreaked havoc across the seas. 25 years before the main events, Shiki found out that Gold Roger had found a very powerful weapon, and he wanted to combine their powers to rule the world. Roger refused, saying that there would be no point in being a pirate if he couldn't do as he pleased, and an epic battle known as Ed War commenced, with Shiki being backed up by his massive crew of 51 divisions. However, due to unexpected stormy weather, the Shiki pirates suffered heavy loses and Shiki ended up with part of a ship's steering wheel stuck in his head.
When Gold Roger was arrested, Shiki attacked Marine Headquarters at Marineford, refusing to believe those wimpy Marines could have captured and arrested a man as powerful as Roger, and demanded that Roger show himself so that he could kill Roger himself. Then Marine Admiral Sengoku approached him, Wengoku telling him that he will never get the chance to fight Roger again, and that he will be executed in his hometown, Loguetown, located in the East Blue. Shiki is greatly upset by this, saying that the East Blue is the weakest of the seas, and that having Roger be executed there would be an insult to a man of his caliber. Marine Vice Admiral Monkey D. Garp then appears and tells him that the East Blue is a symbol of peace, while Sengoku tells him that he will not interfere with the execution. Shiki then engages Sengoku and Garp in an unseen battle, in which half of Marineford is destroyed, Shiki loses, and is inprisoned in Impel Down.20 years before the current storyline, Shiki became the first person in history to escape Impel Down, but cutting off his shackled feet and flying away using his Devil Fruit abilities. He used his twin swords, Outou and Kogarashi, and new, prosthetic limbs. He then approaches Edward Newgate, more commonly known as Whitebeard, and offers to join forces with him to rule the world, but Whitebeard brushes off his request. Shiki lets Whitebeard in on his plan to show the new rookie pirates real fear of pirates. He then moves to an unexplored mountain, talking to his minion, Dr. Indigo, about the experiments taking place and how long until his plan will take. Dr. Indigo informs him that it will take 20 years, at least, for the plan to take action. Shiki accepts this, and declares that in 20 years, he will unleash "Hell" on Earth.
One of Shiki's main powers is his Devil Fruit power: the power of the Fuwa Fuwa no Mi (フワフワの実), which gives him the ability to levitate non-living objects and himself. He can lift many heavy objects, including ships, and is even able to shape various thing (such as debris or Earth) into different shapes, mostly lions heads. The only weakness of this fruit (aside for the normal weaknesses of Devil Fruit, e.i. not being able to swim) is that he cannot levitate living creatures such as people.
Outside of his fruit power, Shiki has a massive crew, which was the biggest pirate crew of all during Roger's time. He also has a huge tolerance for pain, as shown with the steering will being stuck in his head and being able to cut of his own feet.
Shiki also has two swords, callled Outou and Kogarashi. Before his imprisonment, they were used like regular sword, but after he escaped, he used them to replace his missing feet. He is capable of attacking from a distance with them, sending slashes from his swords across the air.