Dragon Ball Z, Vol. 19 by Akira Toriyama

The day of the Cell Game has come - the day when Earth's champions must compete to save the entire human race from destruction. All along, Cell has longed for a match with Goku, to crush the world's mightiest hero and establish its supremacy over all creation. Both of them have enough power flowing through their bodies to destroy the earth. But Goku knows something that Cell doesn't...he isn't the world's mightiest hero. That hero is Gohan, Goku's son...