Calumon is being attacked by a digimon and somehow appears in the real world. Meanwhile, a boy named Takato finds a mysterious blue card. His obsession with the Digimon game leads him to create a digimon, and when he finds a Digivice the Digivice copies his created digimon's data and creates a real digi-egg. He has a strange dream involving a Digimon Tamer (who is Rika), and his digi-egg hatches. He finds his created digimon, Guilmon, and fears getting attacked by him.

Takato secretly sneaks Guilmon into his house and, in the meantime, Rika, a digimon tamer, and her digimon, Renamon, easily defeat a Goblimon. Takato leaves Guilmon alone while he goes to school, but Guilmon follows him and causes chaos in the school. Takato meets Henry and his digimon Terriermon and thinks he isn't worthy of having Guilmon. While looking for a place for Guilmon to stay, Takato and Guilmon are attacked by Renamon and Rika.

Henry and Terriermon stop the fight between Guilmon and Renamon, and Takato finds a perfect hiding place for Guilmon while he’s away. Guilmon and Renamon resume their fight, and Terriermon gets in the way of an attack. He digivolves into Gargomon but can’t control his powers and almost hurts Rika but she is saved by Guilmon.

Gargomon manages to de-digivolve to Terriermon and Henry is left thinking about destroying real living digimon after talking to Rika. He remembers when he first got his digivice. The next day they engage in a battle with Gorillamon, a digimon from Henry's nightmare. Henry refuses to let Terriermon digivolve and he and Guilmon must face the more powerful Digimon without it. Finally, using a Card that ties Gorillamon up, Guilmon and Terriermon defeat him, but he rises again and Terriermon destroys him by firing into his cannon as he charges it, though Henry doesn't let him absorb Gorillamon's data.

Calumon watches kids in Takato’s school play soccer and wishes to be a really good soccer player. He convinces Guilmon to come out of his hiding place and play with him. While they’re in the school, a digital field appears and a Vilemon attacks them. Rika and Renamon save them and Rika still thinks digimon are just data and for fighting.

Rika is disappointed with her mother and with Renamon for not being able to digivolve while fighting Allomon and instead getting help from Guilmon and Terriermon. Renamon goes by herself and meets Impmon, who tells her she doesn’t need a human to make her stronger. When a Dokugumon appears and Renamon is badly hurt. Rika cares for her and she digivolves to Kyubimon and easily defeats Dokugumon with one hit. Kyubimon explains that what finally caused her to digivolve was Rika caring for her.

Guilmon vanishes due to an experiment. Worried about their digimon Henry and Rika join Takato in the quest of rescuing Guilmon without the help of Terriermon or Renamon. The three find and rescue Guilmon and the warp he was trapped in is destroyed by Hypnos as they escape.

Impmon is scaring couples at night in the park, but Takato suspects Guilmon of causing this trouble. Impmon takes Guilmon out and when Takato finds him missing he suspects more of him. When Guilmon comes back, not knowing what's happening, he says he scared a couple and Takato gets really mad at him. Later, Devidramon appears and fights Guilmon and Renamon refuses to join as its Guilmon's fight, not hers. Takato forgives Guilmon after finding out about Impmon, and Guilmon digivolves to Growlmon and destroys Devidramon.

After the battle with Devidramon, Takato tries to make Growlmon de-digivolve into Guilmon, but all to no avail. When it begins to rain, Takato despairs of ever getting his old friend back. However, when the rain ends, Growlmon de-digivolves into Guilmon while watching the rainbow.

Rika is being followed by a mysterious icy force, which frightens her. Not wanting to admit it, she refuses help when Renamon offers to protect her. Renamon is dismissed, and feels hurt by what Rika said to her. While Rika is vulnerable without Renamon's protection, IceDevimon then appears and captures the girl, taking her into an alternate dimension, an icy tomb where he has sealed his Digimon victims. The fallen angel Digimon offers Rika to be his tamer, but she refuses. Renamon comes to Rika's rescue and digivolves to Kyubimon but fails to stop him. Guilmon and Terriermon attempt to help Renamon and Rika, but are trapped by IceDevimon's freezing ice powers. Finally, Henry manages to free them, and Guilmon takes over the battle. Using extra speed and wings, Guilmon traps IceDevimon's head in the ceiling and destroys him, absorbing his data. However, the traumatizing fear caused by the fight causes Rika to claim she hates all Digimon, and she and Kyubimon go their separate ways.

A Musyamon attacks Henry and Takato jumps to the rescue. But Guilmon isn't able to win this battle alone, so Henry has to fight with his own thoughts on the subject of Terriermon Digivolving since last time he couldn't handle the power of Gargomon. When a little girl gets into trouble, Henry acts and Terriermon digivolves to Gargomon. This time Gargomon can control himself and destroys Musyamon. Henry comes to realize that there's just some fights you can't avoid.

Rika and Renamon struggle as they contemplate whether or not they need each other to become powerful. Renamon is attacked by a swarm of hostile Flybeemon, but she defeats her enemies and then considers what Impmon told her about becoming powerful without the aid of a human tamer. Later, she is attacked by Harpymon, and finds herself rendered powerless. Renamon is about to be destroyed, when Rika appears and desperately stabs Harypymon with a tree branch to stop her from harming Renamon, allowing Renamon to escape destruction and digivolve into Kyubimon just in time. Kyubimon easily destroys Harpymon but doesn't absorb her data, as she realizes that Rika's friendship as her tamer is truly what she needs to become powerful. Afterwards, Kyubimon and Rika make amends.

Takato and Guilmon are about to defeat a digimon when Yamaki comes and captures it. Back at Hypnos, they scan the data of the digimon, destroying it and now knowing what Digimon are made of. Armed with this new knowledge, Yamaki prepares to launch the dangerous Juggernaut program to exterminate all the world's Digimon.

As a strange tiger ultimate level Digimon attacks the tamers begin to fight it. However, when it's too strong for both Rika and Henry, Takato uses the power of the blue card to Digivolve Growlmon into his Ultimate form: WarGrowlmon after a mental conversation with Growlmon where Growlmon informs him he is a worthy to be a Tamer after he doubts himself. WarGrowlmon easily beats and destroys the tiger, Mihiramon. Also, Kazu, Kenta and Jeri witness the battle and are impressed by Takato.

Takato is depressed after Henry and Rika have previous commitments and can't go Digimon patrolling, but he feels better when he goes with Guilmon to play with his school friends. But soon the snake deva Digimon attacks, leaving Rika and Henry to fight it on their own, until Impmon helps out and tells Takato they need him. Guilmon and Takato join the battle and Guilmon digivolves to Growlmon. After a short battle, Growlmon mortally wounds Sandiramon with an extra powerful Pyro Blaster, but Sandiramon warns that there's ten more Devas that will be coming before succumbing to his wounds and dying.

During a school camping trip Takato, Henry, Guilmon, Terriermon and Calumon have a fun time relaxing. Even Impmon joins in and has fun. Soon, a series of black outs cause the gang to get suspicious. It turns out a Rooster Deva Sinduramon is absorbing electricity and using it for power. The Sinduramon heads for the dam for more power but proves no match for Gargomon and Growlmon and is destroyed by Growlmon who blasts him into the water causing his own electricity to shock him to death.

Henry was given a worthless card by Kenta's friend Jeramie, but then the card turns into a Blue card when Henry tries to swipe it. When Henry's dad gets home Henry asks if he could check the blue card. While Henry's dad checked it out he notices his old friend Shibumi's code. After Henry, Takato, and Rika go find Jeramie, he tells them that he found the card after bumping into a mysterious man by an electronics store. When Takato and Henry get ready to find the man who bumped into Jeramie, Henry's dad sees them with Terriermon in the park so the kids run away. While Takato, Henry and Rika wait for the mysterious man, they find an Ox and Sheep Deva, Vajramon and Pajiramon. During the battle between Gargomon, Renamon, and the Deva digimons Gargomon Digivolves into Rapidmon to win the battle. Rapidmon destroys Pajiramon the Sheep Deva, but Vajramon, the Ox Deva, secretly reforms himself later and has Renamon come with him to meet with his boss. At the end, Henry's father finds out about Terriermon.

Rika is having a hard time with her mother, who makes Rika attend a photo session with her. Meanwhile, Renamon has been acting distant and it turns out that she has been meeting with Vajramon, who apparently survived the Tamers' previous battle with them. When Renamon reveals that she has been using Vajramon only to obtain information, the Deva becomes outraged and the Tamers fight him in a second battle. The Tamers prove no match for him until Kyuubimon digivolves to Taomon and destroys Vajramon.

Impmon says he hates humans to cover up his own insecurities. While the Tamers are battling the next Deva, Indramon, Impmon decides to battle this Deva all by himself. He fails and is nearly killed. Meanwhile Takato questions on whether or not Calumon is the key to the Tamers digimon's evolution.

Impmon is defeated by Indramon; Indramon then seems to self destruct willingly. Mr. Wong is introduced to the Juggernaut program and is asked to help destroy the Digimon. Indramon rematerializes, and the Tamers commence battle. The Tamers prove no match for Indramon and he isn't even scratched by theirs or the military's attacks. In a desperate move, Takato tries the Blue Card his friend Kazu made for him and Growlmon digivolves to WarGrowlmon again. WarGrowlmon easily destroys Indramon leaving Kazu very pleased with himself.

Jeri and her friends go to find Takato, as they hide and discuss how they would be great tamers Jeri drops an impressive collection of digimon cards on the ground. Jeri meets up with Calumon decides she really could be a Tamer and Calumon should be her partner. Calumon is obviously surprised by Jeri's daydream and while reacting to it the Rat Deva Kumbhiramon bioemerges from the ground. They are saved from the Deva by Leomon and Jeri falls in love with the lone warrior. Leomon is weirded out by her plea to be partners and runs away and hides. Takato meets up with Leomon and Leomon confesses he knows nothing about Tamers or partners. Jeri returns and Leomon runs away again. As Jeri is chasing him Takato calls Henry and Rika who come to the park. Kumbhiramon shows up again and Leomon and Gargomon fight him. Jeri tries to use Digimon Cards on him through Takato's Digivice but fails and becomes depressed. Leomon is angered by this and after Gargomon weakens the Deva, he destroys him. Leomon leaves before his sympathy for Jeri can make him stay.

A string of earthquakes are disturbing the city. The friends meet at Guilmon's hideout and while Rika helps Jeri learn about digicards Henry shows everyone that the devas are patterned after the Chinese horoscope animals. A weird boy who has been secretly watching Calumon comes into the open and the kids run after him. When the Pig Deva – Vikarylamon appears Yamaki freaks out again and initiates the Juggernaut program despite Henry's dad protesting that it will hurt the children's good digimon. The partners track the Pig Deva down but even after digivolving to Growlmon, Gargomon, and Kyubimon they are unable to affect the deva at all. Wishing for help, the tamers find that if they wish to protect others they can matrix digivolve.

The pig deva keeps ploughing through the city and it has to be evacuated. Takato's parents are very concerned because they can't find him but have to evacuate as well. The tamers find themselves outmatched even at matrix level. Henry suggests that he and Rika try believing in themselves and they use Radiant Faith Activate cards. Rapidmon and Taomon knock the Pig Deva down but before they can finish the job the Juggernaut program starts affecting all of them. Henry's dad decides he's had enough and uses his Tai Chi to take down two guards and reach his son. An encrypted code starts attacking the Juggernaut program and as it does the strange child who the kids keep running into reveals himself to be the Monkey Deva and that Calumon is the key to digivolving. At the same time a shining light finds Impmon in the underground tunnel where he's been sulking and offers Impmon power and knowledge to digivolve. The Monkey Deva throws a ball into the Juggernaut tunnel and destroys the program. The pig deva recovers as do Rapidmon and Taomon. Henry's dad and friends reach Takato and the others and tell them about the monkey deva. Takato decides to not be afraid anymore and shows Rika and Henry that if they fight alongside their partners then they can be even stronger. Takato's determination causes WarGrowlmon to gain more strength and after the others deal with Vikarlamon's attacks, WarGrowlmon destroys him with a point-blank Atomic Blaster. Unfortunately, right after, the Monkey Deva, Makuramon, kidnaps Calumon and declares he is taking him back to the Digital World. Leomon tries to save Calumon but is forced back by some shining needles; Jeri receives a Digivice and heals Leomon who is now her partner. In the wake of Vikarlamon's destruction, the Tamers desperately search for a way to enter the Digital World to save Calumon. Hypnos is also destroyed when Makuramon overloads Juggernaught.

Guilmon finds a portal to the digital world in his shed and the kids decide to tell their parents various things: Takato introduces Guilmon to his parents and although his mother freaks out, his father shows a lot of faith in him and convinces his mother which touches him, Henry tells Suzie the truth about Terriermon and leaves his father an e-mail, Rika's grandmother accidentally finds out about Renamaon but takes it well and promises to help cover for Rika. Rika wears a dress for her mother (something she hates to do) in order to give her mother a moment of happiness before she leaves which touches her mother. Jeri gets Leomon to speak to her father about the whole thing and Kazu and Kenta decide to join them in order to find their own Digimon partners. The kids, after getting detention, write essays for Ms. Asaji about what they're doing believing she won't read them for a while, but she reads them right away and confronts them. The kids convince her to leave them to do what they have to do, but she is incredibly worried about them. The next day as they prepare to leave, the group is confronted by Yamaki, but instead of trying to stop them he gives them a comlink to stay in touch as he is now on their side. Afterwards the group heads through the portal to the Digital World.

Once the gang enters the digital world Rika spots "satellite" hoping Calamon would be there so they walk along trying to find Calumon but it turns out that the satellite Rika saw were Rock. Just then Meramon attacks and the gang gets separated into two groups: Takato, Guilmon, Henry, Terriermon, Jeri and Leomon in one group and Rika, Renamon, Kazu and Kenta in the other. Meanwhile, Calumon and Makuramon also get separated.