Dark Spore

Dark Spores (Dark Seeds in the Japanese version) are an evil device that slowly drives their human hosts mad while increasing their intelligence and athletic ability. They grow into Dark Flowers and eventually Dark Trees.

Origin
The first known Dark Spore came into being during Ken Ichijouji's first adventure in the Digital World. When Milleniummon was destroyed, his data turned into Dark Spores and one buried itself into Ken's neck, exerting its influence on him. Since then, it grew within Ken and was later harvested and implanted into other children by Yukio Oikawa.

Uses
Dark Spores slowly and subtly increase the intelligence of their human hosts to genius levels as well as greatly increasing their athletic abilities. However, just as they increase the abilities of their hosts, they also slowly drive them insane and hateful and can drastically alter its host's personality. The effects of the Spore can be negated, however, such as when Ken realized that he had done evil things, and later on when he befriended the other Digidestined.

When cloned, the Spore will eventually bloom into Dark Flowers and will grow from there into Dark Trees, killing the human host. When Yukio Oikawa implanted the Spores into several children, however, he harvested the Dark Flowers before they could become Dark Trees. Knowing that Dark Spores fed off the innocence that allowed a child to travel to the Digital World, he intended to use them to travel to the Digital World himself. In actuality, he was being controlled by Myotismon and he used the Dark Flowers to gain power and become MaloMyotismon. He deceived Oikawa into going to a world made up of wishes in an attempt to finally kill the Digidestined before he was killed himself.

In addition to this, Daemon was also interested in the Dark Spores (specifically, Ken's), 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 many Dark Spores. One was about to hit Ryo, but Ken pushed him out of the way. When he did that, the spore infected Ken 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 from other humans and felt 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 second generation Digidestined, and 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 effect on Ken, and he returned to his original, gentle personality. His memories, however, remained fuzzy and he never seemed to fully remember 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 of his Spore, however, would grow to become Dark Flowers, something Oikawa sought. Oikawa eventually revealed that he had manipulated Ken into becoming the Digimon Emperor and building the Control Spires, knowing that Ken was vulnerable after the death of his brother, Sam Ichijouji.

Noriko
Noriko'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 Takenouchi so they could find Oikawa. When Davis Motomiya encouraged the infected children to believe in themselves, Noriko 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.