As was explained by Bulma in the latest Daima episode, Vegeta apparently trained his way to the new form, doing so on his own which threw Goku for a loop. For Son, the transformation was learned ...

Despite the fact that Goku and the Z-Fighters were transformed into children thanks to Gomah’s wish, Son already demonstrated that he was able to call upon the strength of both Super Saiyan ...

͏ For volume 42, Oda combined the adventurous feel of both series, showing Goku in space with a UFO and a big smile similar to Monkey D. Luffy’s. Oda’s tribute is a fitting conclusion ...