Digimon, huh? Sounds fun. It's been forever since the last time I watched it. Heck, I don't think I watched any Digimon after Frontier so uh... I hope that won't be too much of a problem xD
About the transforming-into-a-digimon-thing, does everyone get just one memory card or can they obtain more (not too many of course) so they can transform into whatever Digimon is suited best for the situation they're dealing with?
Hm. So something or someone is a threat to the Digital World, right? The Digidestined were chosen for a reason, after all. If there is going to be a main villain, are they a powerful and feared Digimon or is the Big Bad a human?
Okay, here are some (kinda silly) things I could think of. Maybe you like nothing on this list but maybe it could help you with coming up with some ideas of your own.
- someone (or even multiple people) knows about the Digital World and the Digimon and fears that they could be a threat to the human world for one reason or another and wants to destroy the Digital World
- similar to the first idea, only this time that person tries to "weaponize" the Digital World and Digimon. Maybe they are greedy and power-hungry or maybe they are a well-intentioned extremist. I dunno.
- an evil and powerful Digimon (let's call it Villain 1) , self-proclaimed ruler of a not so small part of the Digital World and able to corrupt other Digimon
- adding to that, another bad and power-hungry Digimon (Villain 2). Pretends to be an ally to the Digidestined (doesn't look evil at all in its weaker form so I guess it could get the Digidestined to trust it) and wants them to find some legendary thing (no idea what that could be) that makes it strong enough to take down Villain 1. Oh, and Villain 2 claims that that Thing has the power to free the corrupted Digimon. In truth it has the power to do the opposite, it gives Villain 2 the power to corrupt even more Digimon than Villain 1 ever could.