Even though the character was created by Namco Bandai for the game, the company explained how the character was designed by Dragon Ball creator Akira Toriyama.
Namco Bandai created the game’s story and decided what kind of character Android 21 would.
Essentially, Namco Bandai created the framework, and within those parameters, Toriyama designed Android 21.
I asked why the Android 21 trailer read “Original character supervised by Akira Toriyama.”