I made a 100% combo with Dark Phoenix! =D
a.S -> M -> c.M -> H -> f.H -> S -> a.M -> a.M -> a.H -> af.H -> a.S -> Air TK Shot L -> H -> S -> a.M -> a.M -> a.S -> Air TK Shot L -> TK Overdrive H -> Phoenix Rage
The amount of damage varies due to the feathers, but it averages out to about 1,210,000, which is enough to kill any character. I tested this on Viewtiful Joe, so I think this combo is universal.
This combo has a lot of quirks to it, actually. For one thing, during my first ground series I can't do H -> c.H -> f.H because sometimes the f.H feather interrupt the S, so I omitted the c.H. Another thing is that on smaller characters I need to jump straight up (not diagonally) during the first air series or else the a.S won't connect after the af.H. Yet another thing is how during the second air series I can't do an a.H because the a.S doesn't come out in time after the a.H hits, which is weird because I expect the a.H to have more hitstun than the a.M, but whatever.
So yeah, I'm excited to discover my own combo for once instead of copying what I've seen others do.