[@JDubs] If you wanted to use a line based off of the Spirits, you're quite welcome to, but as RBY said it's absolutely not required; all you need for a basic line is three Digimon who form an aesthetically and/or thematically convincing Human, Beast and Double Spirit set? To piggyback on their example, Leomon -> LoaderLeomon -> HeavyLeomon would be a perfectly valid line!