A young man (Yuto) seeks out Hiro's help when a string of acquaintances are attacked and their limbs are changed to plant-like vines. Yuto had noticed Hiro from Ruli's site, Lirurun, which investigates unusual phenomena.
After the visit with Yuto, Hiro, too, is attacked while doing his laundry at the dorm. Thankfully, Gammamon and Kiyoshiro race in before Hiro could be given the drop of plant poison that would change his limbs. The culprit disappears before Gammamon could give chase.
Not long after Hiro's encounter, Team Lirurun meet with Yuto at his family's flower and plant shop. After speaking with Yuto a bit, Kiyoshiro is attacked. "Fifteen minutes," the culprit said. He is saved by the others just in time.
Evening falls. Everyone sleeps in a tent while Kiyoshiro has guard duties. Yuto's bot, GW-1 ( Go well number one), approaches him. A plant Digimon emerges from its eyes and grabs both Kiyoshiro and Yuto! The others give chase. The assailant is the Digimon, Ajatarmon, an ultimate level.
Ajatarmon takes the boys to a secluded area and ties them up. He shows them images of Yuto from GW-1's camera saying that Yuto was the only one to talk to him when he first came to this World. The fact is...he is GW-1. Ajatarmon loves Yuto and wants to turn him into an Ajatarmon. First, Kiyoshiro must be his last test subject.
One third of Kiyoshiro is turned into an Ajatarmon when Hiro and the others arrive. Gammamon and Angoramon evolve to Betelgammamon and Symbaagoramon to fight. As an ultimate, Ajatarmon is tough. Jellymon evolves to Teslajellymon. The three Digimon work together to bring down Ajatarmon and release Yuto.
A beaten down Ajatarmon approaches Yuto. If Yuto cannot be an Ajatarmon, then he will become human. However, that didn't go well, and his limbs begin to fall off as he disappears forever. Ruli and Hiro resolve to look after Yuto for a while to make sure he is ok.
The last scene is Jellymon attempting to give Kiyoshiro an injection with an antidote created by Mummymon, which would return him to normal.