Dragon Ball Z, Vol. 16 : The Room of Spirit and Time Volume 16 by Akira Toriyama

Sci-Fi martial arts action! After years of training and adventure, Goku has become Earth's ultimate warrior. And his son, Gohan, shows even greater promise. But the stakes are increasing as even deadlier enemies threaten the planet.

DRAGON BALL Z is the ultimate science fiction-martial arts manga. Cell has fused with android #17, becoming practically invincible--but not for long! Training in the Room of Spirit and Time, where a year passes for every day outside, Vegeta and Trunks have gone beyond the Super Saiyan, reaching a level of power even greater than second-stage Cell! Now Cell is the one who is outmatched--but Vegeta hates a boring fight. Succumbing to his pride, Vegeta agrees to help Cell fuse with android #18, the last element he needs to become "perfect," so he can have the honor of defeating the strongest being in the world!