The Tags were mentioned by Gennai to the Digi-Destined after they defeated Devimon in Episode 14-"Departure For a New Continent". He informed the Digi-Destined of a greater evil they have yet to face, and that their Digimon must Digivolve further, into their Ultimate forms, if they wish to defeat this evil. However, to do this, they must find their tags and crests, and be able to use them properly. He informed them that the crests were scattered across the continent of Server, but the tags were hidden in a secret location. With this new information, the Digi-Destined prepared a raft to set off to the new continent.
However, on the way, they encountered rough seas, and an even rougher Whamon, who was struck by a Black Gear. Swallowing the kids, and almost killing them with his digestive acid, he was saved and returned to good. Upon further learning of the Digi-Destined's quest, he recalled seeing something being hidden in an Underwater Cavern. He took them there, and as they explored, they found a Drimogemon, also struck by a Black Gear, as well as a small general store. Upon defeating Drimogemon, as well as their own exploring, they found a chest which contained all 7 tags.
Though the location of Kari's Crest and Tag were not revealed, they were first seen carried by Myotismon's henchmen in Episode 30- "Almost Home Free" as he was searching for the 8th Digi-Destined as well, making sure that the only thing that could stop him, the combined power of the Digi-Destined, could not stop his path to rule the world. Myotismon made copies so each minion could search the city to find her faster. However, he kept the real one with him, which was not recovered until Wizardmon stood up against him in Episode 37- "Wizardmon's Gift", to help out his friend Gatomon, Kari's digimon. The Crest was used in the same episode and Gatomon digivolved into Angewomon to defeat Myotismon in his Ultimate form.