S1·E25 Kurata's Revenge

Kurata's true ambition is the total annihilation of the Digimon race, making it come about with the aid of his artificially made puppet Digimon Gizumon AT. The DATS and their Digimon partners fight back to no avail; however, Marcus refuses to give up. Fed up with Marcus' stubbornness, Kurata evolves Gizumon into its Ultimate form, Gizumon XT, to finish the DATS. As a dying act of courage, Merukimon sacrifices himself to teach Keenan that a world where humans' and Digimons' hearts become one is possible. Taking Merukimon's words and the happy memories spent with Marcus and the others to heart, Keenan's DNA explodes, allowing Falcomon to access his Ultimate digivolution, Yatagaramon.