Akira Toriyama had a valid reason for creating a major Dragon Ball character and it is connected to Goku.
Akira Toriyama's Favorite Dragon Ball Character (It's Not Goku)
Character introduction is an important aspect of any anime or manga series because it sets the tone for the character and their future in the story. However, in the case of Dragon Ball, Akira Toriyama had a different approach when introducing characters. Although there's a chance fans may not have noticed, Toriyama had a habit of introducing characters in pairs.
Whether it's Beerus and Whis, Vegeta and Nappa, Tien and Chiaotzu, or Yamcha and Puar, Toriyama always made sure that most of the characters had a supporting character along with them that would help them establish their role in the Dragon Ball story. Even the main character of the series, Goku, had a character created specifically by Toriyama just to connect with him.
This character was none other than Bulma. Although Bulma and Goku's relationship could have seen some distance, when the series started, the two were very close and had a unique bond that highlighted both characters.
