Tekken developer and Executive Producer of Tekken 6 Katsuhiro Harada said, "The number of playable characters will be bigger than Tekken 5 and be the largest roster in the series. I've been on the Tekken series for over 10 years, and one thing we have particularly focused on after Tekken 3 is making sure each character is unique and doesn't overlap with other characters. They all are unique not only in their appearance but their personality and techniques as well."[14]

Harada has stated that Tekken 6 will boast the greatest number of characters ever seen in a Tekken game with a total of 42 characters, including virtually all of the characters from Tekken 5: Dark Resurrection and the two new Bloodline Rebellion characters. According to an Update article in the PlayStation Gallery section on page 40 of the May 2009 issue of PlayStation: The Official Magazine players are able to customize the characters and take any non-customized or customized character online.

Eight new characters are introduced in this game. The first character, Zafina, is a female who enters the tournament to prevent the clash of the "two evil stars".[9] The second character, Leo, is a German fighter who is intended to be a character which can be played by beginners and experienced players alike. The death of Leo's mother, presumably at the hands of Kazuya Mishima prompts Leo to begin investigating the Mishima Zaibatsu.[9] The third character, Miguel Caballero Rojo, is a Spanish matador with a passion for fighting, but no real discipline. Miguel wants to exact revenge upon the death of his sister at her wedding. The fourth character, Bob, is an American who was known as a martial arts genius. Due to being unable to defeat larger opponents however, he disappeared from the fighting world, determined to increase his weight and power while still maintaining speed. Bob enters The King of Iron Fist Tournament 6 to test his new skills and size. The fifth character, NANCY-MI647J, is the bonus boss of the game. NANCY is a giant robotic creation of Mishima Zaibatsu similar as the Jack robots. The sixth character, Azazel, is the final boss of the game. Azazel's story is said to be related with Zafina and Julia Chang's story in Tekken 6 and the confrontation between Jin Kazama and Kazuya Mishima (presumably the 'two evil stars' from Zafina's story). In the console version, the seventh character is Alisa Bosconovitch, a cyborg with jet wings and spinning limbs who may be the cybernetically-enhanced daughter of Dr. Bosconovitch, and can also use her own arms and head as weapons, she was created to serve Jin Kazama. The eighth character is Lars Alexandersson, an unknown descendant of Heihachi Mishima, presumably an illegitimate son.[15]