Dark Spore

Dark Spores are an evil device that slowly drives their human hosts mad while increasing their intelligence and athletic ability. When cloned, they will eventually bloom into Dark Flowers and will grow from there into Dark Trees, killing the human host. The first known Dark Spore came from Milleniummon, after he was defeated. The Dark Spore buried itself into Ken Ichijouji's neck. This Spore was later harvested and implanted into other children. Yukio Oikawa harvested the Dark Flowers, intending to use their power to travel to the Digital World, but was in actuality being controlled by MaloMyotismon to restore him to power.

Daemon was also interested in the Dark Spores, but he was sealed within the Dark Ocean and his reasons for wanting them were never revealed.

Ken Ichijouji
During his first trip to the Digital World, Ken met another Digidestined, Ryo Akiyama. Together, they fought and defeated Milleniummon, but when he was destroyed, he released a Dark Spore. Ken pushed Ryo out its way, but was infected instead. Under the influence of the Spore, he grew to a genius-level intelligence and became very athletic. However, he also began to feel alienated and that the Real World was below him. He decided to take over the Digital World via the Digimon Emperor persona, creating Control Spires and Dark Rings. Eventually, he was defeated by several other Digidestined when he realized that the Digital World wasn't a game and that he had been destroying innocent lives. At this point, it seems that the Dark Spore lost its affect on Ken and he returned to his orignal, gentle personality. His memories, however, remained fuzzy and he never seemed to fully regain his memories of how he was infected by the Dark Spore. Eventually, Oikawa cloned his Dark Spore and gave it to a group of children. Because he had the original Dark Spore, it was able to live inside Ken without hurting him. The clones, however, would grow to become Dark Flowers, something Oikawa sought.

Ken's Dark Spore was never extracted, but he speculates that it was negated by his dreams and the friendships he created.

Nariko
Nariko's Dark Spore was a clone of Ken's, but for reasons unknown it bloomed into a Dark Flower faster than the others--it was hinted that her anger towards her parents contributed to this. Because her Dark Flower was harvested early, she was not with the other children when they attempted to go to the Digital World with Oikawa. When the younger Digidestined were fighting MaloMyotismon, she began to feel an unexplained pain. She was brought to the final battle by Sora so they could find Oikawa. When Davis Motomiya encouraged the infected children to believe in themselves, Nariko admitted that she always wanted to be a kindergarten teacher. She was partnered with a Punimon and gained a red D-3.

Others
None of the other infected children were named, but several had recurring roles and there were at least seventeen total. Davis inspired all of them to believe in themselves and chase their dreams. They all gained digimon partners and digivices.