Dr. Gero sends Android 16 into the past so he can fight a younger, weaker Goku. Android 8 tries to protect Goku and Goku tries to help Eighter. Goku is then hurt, causing Eighter to go into an angry rage, damaging Android 16 and making him unable to fight.
Dr. Gero has just completed his latest Android creation, Android 16. Using the located Time Machine used by Future Trunks to go back in time to warn Goku and the others about the coming android threat, Dr. Gero sets the coordinates to the past when Goku was a young boy. Dr. Gero built Android 16 with a signal objective, to eliminate Goku, no matter what age he is in Android 16 will be able to find Goku. Dr. Gero fires up the time machine and in a matter of seconds Android 16 finds himself in the past, his location being the Red Ribbon Army Base Muscle Tower. Luckily for Android 16, he was sent at the exact moment when Goku was fighting his way through the Red Ribbon forces of Muscle Tower. Before long Android 16 locates Goku, but alongside Goku is another Android who Goku rescued from destruction, Android 8.
Android 16 was ready to commence his elimination of Goku, but Android 8 refuses to let Android 16 harm him. Goku begs Android 8 to get away from him because Android 16 was obviously much stronger than he is, but Android 8 had an objective of his own, and that is to protect Goku no matter what. Android 16 soon realizes that Android 8 is an Android as well, but if he intends to get in the way of his objective then he leaves Android 16 no choice but to terminate his functions. Android 16 does not want to harm Android 8 but he was programmed to eliminate any obstacles standing in the way of his objective. Goku soon decides to battle Android 16 before Eighter is destroyed. For a while Goku is able to hold his own in battle, but Android 16 would prove to be too big of an opponent for Goku to overcome. Android 8 decides to get between the two before Android 16 kills Goku. But Android 8 soon understands that Android 16 really is not that bad of a guy.
Android 16 still clings to the understanding of why he was created and sent back in time. But suddenly Android 16 realizes he is unable to use his true power against Android 8 but yet he is unable to detect any abnormalities to his functions. He starts to wonder if his thoughts circuits were somehow damaged during his battle with Android 8. The battle between the two androids continues, even though Android 8 himself hates fighting. But he still will do anything to protect Goku and Goku agrees with Eighter and feels the same way. Hearing this Android 16 becomes confused on whether Goku is a friend or foe.
Dr. Gero had dedicated his time to building Androids that would kill Goku and through trial and error he discovered something. When Dr. Gero combined his science and technology with Goku's human heart and the ultimate android was born. But his androids made from nothing had unstable human hearts. Android 16 started to wonder if he himself was one of those failed works. Android 16 ignored his confused emotions and continued his battle with Android 8, but Android 8 was not holding back anymore.
Android 8 rammed Android 16, which made him suffer severe damages to his head. Repairs were impossible and he was unable to continue his combat operations. Eighter checked on Goku and found out he was alright. But Goku was more worried about Android 16 which confused 8 because he was trying to kill him. Goku thought it to be amazing that there was someone out there that was so strong. Goku vowed then to train harder so that next time he would be able to beat him by himself. Goku even now realized that Android 16 was not a bad guy. Android 16 is a machine not a person, but there are mysteries in this world. Android 16 soon realized that the cause of these emotions was due to his human heart. He looked forward to seeing Goku again.
Android 16 can be defeated by Goku or Android 8. If Android 8 defeats him before pressing the transformation button after switching from Goku to Android 8 then the dialogue will be different and Android 16 will be killed.
- This scenario bears great similarity to the basic plot of the Terminator franchise, in which an Android (a "Terminator") is sent back in time to kill somebody with an important role in the future. Coincidentally, Android 16 seems to be based on the Terminator, even sounding quite similar in the FUNimation dub.