All throughout DragonBall Series, there has always been something to do with ki, either locating people or ki blasts, or even teleportation. The stronger characters can sense ki from another being. Earlier saiyajins like Vegita and Nappa, had to use devices called scouters to detection how strong someone was. Unfortunetly, these are defective and can not show the actual ki level of a being.

But however, the stronger characters can sense true power with their mind and also control there own power level. This is a good use for fusioning since the two have to be similar is strength. Also we have Tenkaichi Boudoukai since if falls under the category.

        "Tenkaichi Budoukai" is written completely in kanji; if we separate
        the romaji according to each kanji, it would look like this:
        "Ten  Kai  Chi  Bu  Dou  Kai"

        For those with even rudimentry Japanese, you should be able to
        recognize that "Ichi" means "one."  Here's a word-by-word translation:

        Ten - Sky, Heaven
        Kai - Beneath, under
        Chi - (Number) One
        Bu - Martial Arts, fighting technique
        Dou - Way of
        Kai - Meeting

        "Tenka" (Under heaven) is used to refer to "the world," as everything
        in this world is beneath the skies / under heaven.

        "Budou" means martial arts, or "the way (art) of fighting."

        Putting the rest together, a fairly concise translation of "Tenkaichi
        Budoukai" would be "The World's Best Martial Artist Tournament."
 
 

       The 21nd Tenkaichi Budoukai:

          Champion:  Master Roshi (Kamesennin)
          Runner-up:  Son Goku

       The 22nd Tenkaichi Budoukai:

          Champion:  Tien
          Runner-up:  Son Goku

       The 23rd Tenkaichi Budoukai:

          Champion:  Son Goku
          Runner-up: Piccolo

      The Cell Game:

          Champion:  Son Gohan

      The 24th Tenkaichi Budoukai:

          Champion:  Mr. Satan

       The 25th Tenkaichi Budoukai:

          Adult Division Champion:  Mr. Satan
          Adult Division Runner-up:  No. 18
          Children Division Champion:  Chibi Trunks
          Children Division Runner-up:  Son Goten

        Note: In all the tournaments to follow, Mr. Satan is the champion, while Mr.
        Buu is the runner-up..  Basically Mr. Satan cheats in letting Mr. Buu
        fight with everyone else first, and then to throw the match to Mr.
        Satan.