"Dragon Ball Z" was 291 episodes long and often strayed from the original material created by Akira Toriyama. The original anime was being created as the manga was being released, but the anime would often catch up to the manga. This resulted in the need to create filler arcs while more chapters in the manga series were being produced. In an effort to stall for time, the creators of the anime would make entire episodes that revolved around a character -- typically Goku -- charging up an attack without advancing the plot at all. The filler arcs and many of these redundant "charging up" episodes have been cut, leaving the total episode count for "Dragon Ball Kai" at 98, down from the original 291.
The majority of the original Japanese cast was commissioned to re-record certain scenes to improve continuity and get rid of mistakes, such as calling out the wrong name for an ability being used. For example, an early episode in the Vegeta Saga has Goku in his Masenko stance, but he yells "Kamehameha!" instead.
The episodes included in "Dragon Ball Kai" have been completely remastered using the original Japanese film. This includes some continuity errors and off-model coloring. For example, in some of the earlier episodes, Piccolo's blood was shown as red; later in the series, it was established as being purple. In cases where parts of the film had been damaged, some scenes have been re-drawn.
All of the original openings and endings have been cut and replaced with new high-definition animation. The new animations are accompanied by new songs created for the series, including "Dragon Soul" and "Yeah! Break! Care! Break!" by Takayoshi Tanimoto, and "Kokoro no Hane" by Team Dragon, which is composed of members from the group known as AKB48. Much of the original background music has been rescored by Shunsuke Kikuchi, who composed most of the original background music for "Dragon Ball Z."