Dragon Ball, Vol. 08 by Akira Toriyama

Tired of losing their best operatives to Son Goku, the commanders of the Red Ribbon Army hire Taopaipai, the world's greatest assassin, to "take care" of him permanently! To have a chance of defeating this new opponent, Goku must climb the miles-high Karin Tower, where a mysterious hermit guards a jug of magic water which will grant the one who drinks it super strength. And while Goku struggles to get the magic water, time is running out...because Commander Red only needs two more Dragon Balls to make his deepest, darkest wishes come true!