Kouta is the goggle boy of the story. He protected his Digimon, DORUmon, from an Ookuwamon X, and that's when DORUmon evolved to DORUgamon. DORUmon's full evolution line is Dodomon (Baby), Dorimon (Baby II), DORUmon (Child), DORUgamon (Adult), DORUgremon (Perfect), DORUghoramon (Ultimate/Final). DORUghoramon was defeated by Omegamon X, but the X Antibody forced him to evolve further, and it devoured his flesh, causing him to evolve into Death-X-DORUghoramon (Ultimate/Final). However, DORUmon's data was extracted from Death-X-DORUghoramon; Death-X-DORUghoramon then became Death-X-mon (UIltimate/Final), while DORUmon evolved into Raptordramon (Adult), Grademon (Perfect), and Alphamon (Ultimate/Final). He combined with Ou Ryuumon (Ultimate/Final) to gain a set of wings and a huge sword. That form is called Alphamon Ultimate War Blade King Dragon.
Yuuji first appears in the Urd Terminal, the place where dinosaur-like Digimon roam. Yuuji doesn't seem to think much of Kouta's Tamer skills, and he aspires to have a "Perfect Pendulum" - in other words, he wants Ryuudamon to have a Win Ratio of 100% no matter what. Later, when Ou Ryuumon and Alphamon battle Death-X-mon, Ou Ryuumon is badly damaged...but Yuuji and Kouta are fighting to live, and Ou Ryuumon and Alphamon Blast Evolve! Ryuudamon's full evolution line is Fufumon (Baby), Kyokyomon (Baby II), Ryuudamon (Child), Gin Ryuumon (Adult), Hisha Ryuumon (Perfect), Ou Ryuumon (Ultimate/Final). He combines with Alphamon to become Alphamon Ultimate War Blade King Dragon (Ultimate/Final).