The justification for human characters in Dragon Ball Online is that ki control became a more common thing. The reason why it became a more common thing, if memory serves, is Gohan publishing a book explaining it called Groundbreaking Science.
Do you doods think that, sometime down the line, we'll see Gohan lay the groundwork for his scholarly magnum opus?
Do you doods think that, sometime down the line, we'll see Gohan lay the groundwork for his scholarly magnum opus?