TV-Series
Description
In the world of Digimon Adventure 02, Gennai is a mysterious being who serves as a guide and informational source for the DigiDestined. His origins trace back to events before the first series, where he was part of a group that created the Digivices, Tags, and Crests, as well as the partner Digimon for the children. Their secret base was attacked by the Dark Master Piedmon, who slaughtered all of Gennai's comrades. During this assault, Piedmon inserted a mysterious black object into Gennai's back before Gennai escaped with the Digi-Eggs and Digivices. In the process of fleeing, he accidentally lost one egg, which would later hatch into Gatomon, who grew up alone and became an adversary before reuniting with her destined partner.

When the DigiDestined first encounter Gennai after their battle with Devimon, he appears as a short, elderly man with a large gray mustache, a small ponytail, and eyes that are almost always shut. His personality is that of an eccentric mentor. He often provides puzzling advice full of tangents and idiosyncrasies, which can be barely helpful at first glance. However, his knowledge is vast, and he is deeply committed to protecting the Digital World. He is not human, describing himself as being composed of data, but without the same attributes as a Digimon. His core motivation is to guide the DigiDestined in their battles against evil forces and to maintain the balance between the Digital and Real Worlds.

By the time of Digimon Adventure 02, Gennai has undergone a significant transformation, appearing not as an old man but restored to a younger, more vibrant form with short brown hair tied in a ponytail and wearing brown and cream-colored robes. It is suggested that the digital deity Azulongmon was responsible for restoring him to his prime. This younger incarnation is more active and direct in his assistance. He reveals that he and his kind have been working to erase evidence of the Digital World from the Real World. His role in the second series is pivotal during the World Tour arc; he delivers one of Azulongmon's DigiCores to the DigiDestined, which allows the original eight partner Digimon to regain their ability to evolve to the Ultimate level and enables the new form Imperialdramon.

Gennai's key relationships are primarily with the DigiDestined, acting as a behind-the-scenes strategist. He has a particularly close rapport with Izzy, often sending him computer programs and technical information to help analyze the Digital World. In Digimon Adventure 02, he demonstrates an ability to be in multiple places at once, or to have created copies of himself, as his counterparts appear simultaneously in different locations around the world to aid the international DigiDestined. At the conclusion of the series, he returns a significant item to Gatomon, her lost Tail Ring, explaining that its absence was what had allowed her to perform Armor and DNA Digivolution alongside the other Digimon.

In terms of abilities, Gennai does not fight directly in Digimon Adventure 02, but his powers are technological and informational. He can project holographic communications, send data and programs directly to computers, and manipulate aspects of the Digital World's infrastructure. He possesses a deep, historical knowledge of the Digital World, including its previous cycles of conflict and the legend of the first DigiDestined who fought a great evil behind the "Wall of Fire". His most notable ability is his resourcefulness and his role as a keeper of secrets, holding onto powerful artifacts like Gatomon's ring until the appropriate moment. The mysterious black ball Piedmon placed in him remains an unresolved element, though its effects are speculated to be the cause of his aged appearance in the first series.