Digimon Adventure 02-1R
It has been three years since the DigiDestined heroes Tai, Matt, Sora, Izzy, Mimi, Joe, T.K. and Kari saved the Digital World from the biggest threat it had seen to date, and one since Ryo and Ken saved it from Millenniummon. Using their Crests, the heroes sealed the DigiWorld from the real world once and for all, but by the same stroke also cast a protective barrier against it meant to repel other threats. All seemed well.
However, the forces of the Dark Ocean conspired to weaken the barrier between the two worlds again, drawing Ken back into the DigiWorld under the guise of the Digimon Emperor, convincing him to do as he pleases. In the span of only a few months, using dark technology of his own making, the Digimon Emperor enslaved and terrorized most of the Digital World, with no DigiDestined heroes in sight at all. The tables will soon turn, however, as a new wave of heroes and some of the old ones realize what is going on and interfere.
Series Differences: This is a more or less canon iteration of Digimon Adventure 02 (aka the second season of Digimon), with slightly aged up main characters (+1 ~ +3 years, take your pick!). The only major difference (as of now) is that there isn't a time disconnection between the Digital World and the real world (i.e. time flows 1:1). This doesn't apply to the first DigiDestineds' venture (which was pre-Unification), merely to the present and future. Future applicants are welcome to come up with tweaks and changes they would like to have applied to this theme if it isn't suitable right now, though it's suggested to talk to the played cast first to doublecheck.
For reference: the IC date/time is identical to RL, -12 years (so 2014 becomes 2002). Please don't fret calendar woes and just handwave it, but remember this when it comes to technology! (VCR vs DVD, cellphone tech levels, etc.)