The thing about using the Dragon Balls is that not everyone comes back. The Dragon Balls were never meant to bring someone back to life more than once. In fact in the year 470, when Kami originally created the Dragon Balls, it was for that purpose and that purpose only. Kami felt guilty of the damage that Garlic and his "other half" King Piccolo did on the world and wanted to fix it.
Few ever spoke of the event where those who were slain were revived. The various cultures around the world just shrugged it off as a miracle from God. It was simpler times back then. As opposed to allowing the Dragon Balls that once time use, Kami decided to keep them active and allow for various tales and folklore be spread. Every decade or so a person or a group of people would travel the world and seek the mystical orbs. After all, there was no technology available to easily locate them.
It was around the year 750 that the Dragon Balls started to get heavily used. Even more so, they were used for mass revivals once more. But unlike back in 470, they began to be used for this purpose more often. This became an issue as Kami designed the Dragon Balls to bring back many people at once, but not more than once. In a more technologically and well connected society, such revivals began to be recorded.
The first such event, originally labeled as The Rising, later to be known as the First Rising, happened on May 12th, 750. About 500,000 people, who were slain by the tyrannical Red Ribbon Army, rose from the dead. They were known as the First Risen.
It wasn't until the Second Rising on May 14th, 753 that the world began to realize that not everyone comes back. This time about 1,000,000 people returned to life after being victims of King Piccolo and his children. However, 40,000 of such victims were not so lucky as they were First Risen.
And so such a trend continued. Almost nine years later on Christmas Eve 762, almost a month after East City and its population of 300,000 were wiped off the face of the earth, a miracle happened as the city and its people was suddenly restored...for the most part. Approximately 5,000 people were left out of the Third Rising, as many of those who did not return (including Earths military forces) were previous Risen.
It only took a year for the Fourth Rising to take place, with the largest rising yet of about 10,000,000. This was right after the world was suddenly plummeted to chaos and the people of Earth temporarily became rabid cannibals due to some an airborne infection known as the Z virus. This time about 250,000 of previous Risen did not return.
The Fifth Rising seemed to happen with the direct defeat of Cell where close to 20,000,000 people he supposedly made "disappear", as well as a few residents of South City who claimed to be killed by robotic men, suddenly reappeared. Of course, around 5,000,000 more were never to be seen again.
An example of someone who was never to be seen again was a young woman named Luci. As a child Luci Miguel was unfortunately killed when King Piccolo was on one of his rampages. She was Second Risen. Years later while shopping one day in East City, a married Luci Satan happened to be at the wrong place at the wrong time. Killed by a man from space named Nappa leaving behind a young daughter named Videl.
It was after the second death of his wife as well as witnessing some former World Martial Arts Tournament fighters attempt to bring justice to the murderer that Mr. Satan decided to pursue a career in martial arts so that should such a monster show up again, he could stop him. Of course after training for several years trying to emulate those fighters and their techniques with no luck, Mr. Satan began to think everything that happened was a trick, especially upon noticing the fighters' close relationship with the Briefs family and had heard of their many "experiments."
So he decided to take a different approach, train on his own. Open up schools and learn from his students. And so he did, gaining fame and fortune especially after he and his students successfully defended an elementary school from people infected with the Z virus attacking. When the monster named Cell did appear, Mr. Satan was ready to stop him. He felt like he was on top of his game after winning the World Martial Arts Tournament, even though he was disappointed in his competition as he wanted to confront the so called "tricksters" who had participated in previous tournaments and defeat them "fair and square."
When Mr. Satan showed up with his entourage, he saw as these former combatants "flew" in. He decided to confront Cell as his own way of showing up the "tricksters." One miserable failure, and several high powered fights between Cell and blond men later, all of the fighters were gone. Some died including the former WMAT champion and a purple haired teen. And the rest disappeared. It was at that moment that Mr. Satan realized his opportunity and with his selfish decision he changed the world forever.
A/N: I made it a point that the wish to the Dragon Balls made while Goku was fighting Frieza brought back everyone killed by the PTO, not just Frieza, but Vegeta and Nappa as well. This fixes the plot hole which is the fact the it appears in canon that the people in East City were never brought back to life, as well as the one Namekian village Vegeta slaughtered. And while that means Yamcha and Tien did get revived a few months earlier than canon, who really cares? Another example is the use of Dragon Balls during the RRA arc (reviving all killed by RRA and associates, not just Bora) and the Garlic Jr. arc (which were not used on screen). Also, I'm pulling dates out of the Dragon Ball Timeline on site. Did you know the fight against Frieza took place on Christmas eve? Gives the phrase Frieza Day new meaning.
Also, anyone else scratching their head about the new movie? I don't get how the dragon can bring back Frieza, many years after his death, as living chunks. Usually when the dragon brings someone back whose body was destroyed, everything is in tact (e.g. Krillin isn't ash, Tien has his arm back, people are not candy, etc). Also did we forget that one year rule? With that logic the wish in canon to bring back those killed by Frieza would have brought back most of the Saiyan race and many more. Then again this is the same series which brought is Bio Broly...because reasons!
