The film begins with Goku (Justin Chatwin) and his grandfather (Randall Duk Kim) standing on top of a clothesline. They spar and both appear to be great fighters. The training session ends and Goku and his grandfather (Granpa Gohan) go inside to talk. Goku mentions being harassed at school about being different, and how he could easily tear those guys apart, but of course this is not why Gohan taught him how to fight. Goku relents and asks instead, that he teach him something useful, like talking to girls, as he does not seem to be able to do so without looking like an idiot.
As Goku prepares to leave, Gohan gives him a box, and wishes him Happy Birthday. Inside the box, is a Dragonball, the fourth one (it has four stars). There are only seven others in existence. Gohan tells him that alone, it does nothing, but when gathered along with the others, it will grant the holder “one perfect wish.”
Goku arrives at school and is quickly accosted by several school bullies who try very hard to provoke him, calling him “Ginko” or something. Before things can get out of hand, Chi Chi (Jamie Chung) shows up and calls out to the bullies, whom she seems to be friends with, and they leave.
Cut to an airship of some sort, with a menacing figure in a black cloak its Lord Piccolo (James Marsters). Lord Piccolo creates a red energy ball and releases it, watching as it dives towards the ground, as if following something. The red energy ball continues until it reaches the ground, somewhere in a devastated region of Japan. Among the ruins, a young woman takes a little girl by the hand and they attempt to hide from someone who is pursuing them. The young woman appears to have a round object hidden in a pouch. Out of the smoke comes Mai (Eriko Tamura), who appears to be pursuing the young woman and the child. The woman and child hide beneath the floorboards but it appears that Mai has found them. In order to protect the child, the woman reveals herself and gives Mai the dragonball. Mai points her gun at the woman, just as Lord Picolo arrives. A gunshot is heard, but not seen, and the scene cuts to a projection of a solar eclipse shown in Goku’s class.
In class, Goku doesn’t seem to be paying much attention, but instead, spends his time staring at Chi Chi. As the teacher talks about theological implications of the impending solar eclipse, Goku fantasizes about Chi Chi. This starts a short bit of hallucination/daydreaming as he imagines Chi Chi in a field eating a strawberry rather seductively. His fantasy is quickly interrupted by his teacher who asks him what the solar eclipse means. A startled Goku replies that his grandfather told him to beware of the Nemecks, a race of aliens who tried to destroy the earth 2000 years ago. This draws some laughs, but he gets off the hook.
Between classes, Chi Chi is unable to open her locker (her key card doesn’t seem to work). Goku attempts to help by using his Chi powers, but isn’t able to control it very well, causing all the lockers around Chi Chi to burst open, tossing books and papers everywhere. Goku makes and run for it, but Chi Chi catches up to him and confronts him about the lockers, and seems to know that he used his “Chi.” Goku is slightly surprised that Chi Chi knows about his powers. This begins a rather awkward conversation with Goku verbally stumbling all over the place, but ends with Chi Chi inviting him to a party she is hosting. Goku is more than enthusiastic about attending.
At home, Goku is nervously practicing his “hellos” in front of the mirror. He tries slicking back his hair, but it ends up popping back into its trademark spiky look. Goku leaves for the party, not realising that Gohan had prepared dinner and a cake for his birthday.
Goku tries to get into the party, but the school jocks won’t let him in, with more physical and verbal bullying. The lead bully takes a swing at Goku and misses (Goku is too fast for him). Everyone lunges at Goku, and ends up hitting each other instead, since Goku intends to hold his promise of not fighting. The bully from earlier arrives to see his goons all wiped out, and proceeds to go at Goku with a baseball bat, only succeeding in smashing the crap out of his own car. More fighting ensues and the bullies are finally vanquished (by each other). Chi Chi seems impressed.
Goku and Chi Chi go off to talk, and she tells him that he and she are very much alike -much to Goku’s confusion. Goku reveals that he didn’t have parents, and doesn’t know much about them. He also notes that his grandfather had told him that all would be revealed to him when he turns 18, which is that very night.
Back at the house, Gohan is having dinner alone when Mai attacks him. He is able to dodge her attacks, but Piccolo arrives and disables him. Realizing that the Dragonball is not there, he leaves, collapsing the house as he does, with Gohan still inside.
Back at the party, Goku realizes something is wrong and runs home. He is able to find his grandfather, severely injured. Gohan tells him that Piccolo has returned and seeking the dragonballs. Fortunately, Goku had the dragonball on him the whole time, so Piccolo was not able to get to it. Gohan tells Goku to find the other dragonballs before it’s too late, and tells him to have faith, then dies.
The following day, Goku buries his grandfather and returns home. Among the rubble, Goku finds another present Gohan had left him, an orange fighter’s robe/uniform (the one Goku is known to wear in the anime). Goku hears a noise and turns to stare down the barrel of a gun, held by Bulma (Emmy Rossum). Goku questions her about Piccolo (and whether she was Piccolo), but she doesn’t seem to know anything about him, however, she has come to find something that was stolen from her father’s corporation, a “promethium orb”, as she calls it. A device clipped to Bulma’s belt rings, indicating that it is nearby and she sees that Goku has it, the dragonball. They fight for the Dragonball, both falling to the ground, but with Bulma still pointing a gun at Goku’s chest. Bulma reveals that her father found the promethium orb twenty years ago, and that it was stolen last night. She describes it as having 5 stars, but to her surprise, Goku reveals his dragonball to have only 4 stars.
Bulma realizes the mistake and puts the gun away, but asks what price Goku is willing to accept for the dragonball he has, who replies that it’s not for sale. Goku asks about the Dragonball Bulma is after, and it turns out that the night before, someone broke into her father’s company, Capsule Corp, killed the guards, and made off with the dragonball. The two talk some more, and Bulma reveals that she wants to find them all, and use them to provide an unlimited source of free energy. She intends to track them down using a device she invented, which detects the energy released from the dragonballs. Goku proposes that Bulma help him get to Master Roshi (mentioned by Gohan before dying), in return for helping her find the other dragonballs. She agrees. Outside, Bulma places a small capsule on the ground, presses a button on her keys and it transforms into a full sized ATV.
In the city, Bulma attempts to search the public directory for Master Roshi, but has no luck. However, Goku is able to sense Roshi the same way he was able to sense his grandfather. Bulma’s device goes off, and they pursue the signal to the next dragonball. They find an old house and break in (technically, the door was unlocked). Goku knocks over some chest pieces and attempts to catch them Matrix style, but still wakes up Master Roshi (Chow Yun Fat) who thinks that he is a thief. They fight and Roshi beats the snot out of Goku.
Bulma tries to stop the fight; Goku tries to hit Roshi with a Chi blast, and ends up knocking over Bulma. Roshi realizes that Goku was trained by Gohan and stops, then proceeds to laugh like a crazy person Roshi appears to be a little eccentric. Goku tells Roshi about Gohan’s death and Piccolo’s escape, and Roshi’s expression turns grim. Roshi decides to help and goes looking for his dragonball, and finds it with Goku’s help. Upon touching the Dragonball, Goku receives images of Piccolo, mass destruction, and the face of a gorilla-like monster). Roshi also reveals that a prophecy foretells that in seven days, the eclipse will occur, and if they cannot gather the seven dragonballs before Piccolo does, a massive disaster will occur and the human race will be doomed. Roshi also knows that Goku is the key, that’s why Gohan trained him. The three conclude that their goals are the same, and agree to work together.
Back at the floating fortress, Piccolo causes an entire lake/marsh to evaporate, killing all the living things in it to retrieve a dragonball that was resting at the bottom.
At Roshi’s place, Goku is packing a massive backpack of stuff, while Roshi gets on the ATV with Bulma. Roshi says that he will take Goku to a place where he can learn the ability to control air, fire and water, but in order to learn these abilities, he has to get stronger first, and so he will have to carry the massive bag of gear, and travel on foot.
The three of them take a long journey across the desert, arriving at a stone temple where Roshi will teach him the skills he was taught. However, upon arriving at the temple, it is crowded with fighters, training for an upcoming tournament. They stumble upon Chi Chi, who appears to be quite skilled herself, and is one of the challengers in the tournament. This is what Chi Chi meant when she said that she and Goku are much alike, they are both warriors. However, their reunion is cut short as Bulma picks up on another dragonball and they head for it. They approach the location of the dragonball but suddenly crash and fall into a hole in the road. They are unhurt, but are now stuck in a rather deep hole, unable to get out. Suddenly, a man pokes his head over the top of the hole, and introduces himself as Yamcha (Joon Park). Bulma tries to use her looks and charm to get Yamcha to help, who agrees to, but only in exchange for payment. Roshi notes that it was probably Yamcha who dug the hole in the first place. Yamcha seems to like Bulma’s vehicle, and agrees to help them out if he gets to keep it. Bulma rejects the idea, and the three of them are stuck in the hole overnight, making a camping trip out of it (bond fire and all). Roshi tells the story about how earth was almost destroyed two thousand years ago by Piccolo and Osaru (I think that’s the pronunciation). Seven mystics banded together and gave up their lives to create a spell that would trap Piccolo, but he has managed to escape.
Roshi ends his story, and suddenly, Bulma’s dragonball detector gets a reading. Yamcha pokes his head over the hole upon hearing the noise, and is intrigued. The dragonball appears to be embedded inside the rock surrounding them, and they need to dig through the rock to get to it. Roshi jumps out of the hole (turns out he could have done so the whole time, he just didn’t) and confronts Yamcha. Roshi makes a deal, that Yamcha will be paid well if he helps them get to the dragonball, since he has drilling equipment he used to dig the hole-trap in the first place. After some drilling, then finally get to the dragonball.
The group (now including Yamcha) head back to the temple for rest. Upon their return, they watch a tournament match between Chi Chi and Mai. Mai cheats and cuts Chi Chi’s arm, but then takes a step out of the ring to disqualify herself. Chi Chi is puzzled, but it seems Mai only fought her to take a sample of her blood (important later).
The next dragonball is located deep underground, near a volcano. The good guys search for it, but are ambushed by a dozen or so humanoid monsters created from Piccolo’s blood. However, this seems to be a stroke of good fortune, as Goku is able to use the bodies of the creatures to form a path in the lava in order to get the dragonball. Upon getting to it, Goku is attacked by Mai, but easily knocks her out. Goku and the rest head out and return to the temple.
In the evening, Roshi attempts to teach Goku how to use the Kamehameha, a technique of generating a destructive ball of energy and throwing it at things. Roshi easily produces a golden sphere of energy and lights a torch, then tells Goku that his “homework” for the night is to light all the torches around him, then turns it for the night, leaving Goku alone. Goku attempts to light the torches a few times but fails, finally resorting to lighting the torches by candle, only to be caught by Chi Chi. She notes that Goku can do it, he just needs the motivation, and so she tells him that for every torch he lights, he can take one step closer to her. Almost immediately, Goku produces a Kamehameha and lights one of the torches. His next attempt is far from successful, but with a little bit of motivation (and flirting) from Chi Chi, he lights all the torches in one shot. The two embrace and kiss, with Goku using his new powers to put out all the torches to give them some privacy.
Later that night, Bulma hears a noise outside her room, and goes to investigate, gun in hand. Outside, she sees Chi Chi leaving Goku’s room and they have an awkward moment. They bid each other goodnight, and Chi Chi leaves. Yamcha walks by and speaks to Bulma, and they share a laugh at Goku and Chi Chi’s relationship, until Goku comes in from the outside. They realise that Chi Chi was snooping around in Goku’s room while he was away, realising that she was going for the dragonballs. Goku, Bulma, and Yamcha chase after her. As Chi Chi makes a run for it, she is ambushed by…Chi Chi. Turns out one of them is an impostor (its Mai using Chi Chi’s blood to take her shape). The impostor knocks over a bunch of lamps causing a fire barrier between the others and the two Chi Chis. Goku ignores the fires and leaps through, but doesn’t know who to fight. One of the women is knocked down and pleas for help. Goku, without thinking, attacks the other one but realises too late that she is the real one (after recognizing the scar on her arm). Goku is shot in the back by the impostor, and she escapes.
The rest of the group arrive to find Goku alive, but barely. Fortunately, Roshi is able to channel his powers to heal Goku.
Due to the loss of the dragonballs, they can no longer hope to use them to stop Picolo. Roshi has no choice but to ask Master Mutaito (Ernie Hudson) to help create another prison for Piccolo. Master Mutaito warns that using the vessel will drain the life force from the user, killing him, but Roshi sees no other choice.
The next day, the group (except for Chi Chi, whose still out from being hit by Goku) head towards a mountain where Piccolo will use the dragonballs to summon the dragon to grant his wish. The good guys are all packed into Yamcha’s flying SUV and make their way to the mountain. Piccolo realises that they are approaching though, and fire energy balls at them. Yamcha tries to evade, but they are eventually shot down and everyone is scattered around the base of the mountain.
Goku attempts to confront Piccolo, but doesn’t seem to be able to defeat him. In the crash, the vessel made to imprison Piccolo was dropped, and Roshi attempts to find it. After some fighting, the sun begins to eclipse, and it appears that Goku is mutating. Turns out, he was Ozaru the entire time! Piccolo reveals that Goku was sent to earth in human form, and on his 18th birthday, upon the eclipse, he will transform into an unstoppable monster. Goku, now in Ozaru form, chases the others. Yamcha tells Bulma and the rest to make a run for it, while he holds Ozaru off. Bulma seems impressed (and a bit smitten), and tosses Yamcha one of her guns. While escaping, Bulma runs into Mai, and they fight. They are evenly matched, but Bulma gets the upper hand when she throws her ATV at Mai (while it’s still in capsule form), then activating it, causing the vehicle to materialize, flying right over Mai and distracting her. However, it seems that Bulma has finally run out of ammo and luck. Mai moves in for the kill but is shot in the back by Yamcha.
Outside the caves, Roshi has found the vessel and attempts to trap Piccolo with it. Roshi pours his life force into it and causes a swirling vortex of energy to engulf Piccolo. For a moment it looks like Piccolo is in trouble, but having learned his lesson from his first incarceration, he fires an energy ball downwards into the vortex, destroying the vessel. Roshi is knocked unconscious and presumably dead.
Ozaru is still rampaging about, but upon seeing Roshi’s body, Goku (inside Ozaru) begins to struggle against it. Goku finally realizes what his grandfather said about making piece with both halves of himself, and is able to attain balance and control of Ozaru (his evil half). Goku then reverts to his human form and battles Piccolo. Almost simultaneously, both characters prepare to unleash a devastating attack on each other, with Goku producing a powerful Kamehameha attack. Goku’s attack proves more powerful than Piccolo’s, piercing through his attack and knocking him out of the air. Piccolo drops to the group, unconscious and smouldering.
As everyone recovers their bearings, they realise that master Roshi is dead, but with all the dragonballs in their possession, they summon the dragon and asks it to bring Roshi back. A moment later, Roshi comes back to life, the dragon disappears, and the dragonballs fly away in every direction.
Everything is back to normal - Bulma and Yamcha head off to search for the dragonballs, and Goku goes back to Chi Chi. They talk about how Goku knocked her out, and it was only because she wasn’t prepared, and they decided to settle things the right way, with a tournament. The last scene shows the two in mid-air slow-mo fighting poses.
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