Tanjirō Kamado, joined with Inosuke Hashibira, a boy raised by boars who wears a boar's head, and Zenitsu Agatsuma, a scared boy who reveals his true power when he sleeps, boards the Infinity Train on a new mission with the Fire Hashira, Kyōjurō Rengoku, to defeat a demon who has been tormenting the people and killing the demon slayers who oppose it!

In the distant technological future, civilization has reached its ultimate Net-based form. An "infection" in the past caused the automated systems to spiral out of order, resulting in a multi-leveled city structure that replicates itself infinitely in all directions. Now humanity has lost access to the city's controls, and is hunted down and purged by the defense system known as the Safeguard. In a tiny corner of the city, a little enclave known as the Electro-Fishers is facing eventual extinction, trapped between the threat of the Safeguard and dwindling food supplies. A girl named Zuru goes on a journey to find food for her village, only to inadvertently cause doom when an observation tower senses her and summons a Safeguard pack to eliminate the threat. With her companions dead and all escape routes blocked, the only thing that can save her now is the sudden arrival of Kiri the Wanderer, on his quest for the Net Terminal Genes, the key to restoring order to the world.

Meicoomon vanishes into the distorted abyss. Shaken, Taichi and the others search for answers about Meicoomon's infection. Kōshirō seeks answers from Meiko but she's lost all emotion. Kōshirō quarantines Agumon and the other Digimon in the office so that the infection can't spread any further, but Patamon starts to show signs of the illness. Agumon and the others use Hikari's voice to tell the team about an important secret concerning the Digital World.

Tai is now a university student, living alone, working hard at school, and working every day, but with his future still undecided. Meanwhile, Matt and others continue to work on Digimon incidents and activities that help people with their partner Digimon. When an unprecedented phenomenon occurs, the DigiDestined discover that when they grow up, their relationship with their partner Digimon will come closer to an end. As a countdown timer activates on the Digivice, they realize that the more they fight with their partner Digimon, the faster their bond breaks. Will they fight for others and lose their partner? The time to choose and decide is approaching fast. There is a short time before “chosen children” will become adults. This is the last adventure of Tai and Agumon.

The DigiDestined inaugurate their newest members, Meiko Mochizuki and Meicoomon, with a trip to a nearby hot spring. Meanwhile, Joe is becoming more distant, struggling to balance his duty as a DigiDestined and the competitive world of academics. As the damage caused by Alphamon is slowly repaired, another infected Digimon, Ogremon, suddenly appears, and although they only have good intentions, the decisions the DigiDestined make now will have unforeseen consequences.