Hmm; spindly hair antennae, a flat-ish body structure, floofy sleeves...calling it.
Laharl and Flonne's love child from an alternative future where things go to hell (ha ha). D2's plot is going to be Laharl trying to prevent it from coming to pass while adamantly denying the kid is his.
Either that or a younger-sister-I-never-knew about with Japan's infamous love of Brother-Sister love plots with her competing against Flonne.
What's amusing is since this is the Disgaea-verse I can be completely serious with those guesses.