1: Earn it on any character you want. All the costume parts, trails, auras and emotes are Certificates, which means that you can collect them on EVERY character you have, or make in the future, off one purchase.
2: You have two options with Trail Auras: Always on, or On While Moving. You can't make it turn on only while flying.
@Roderick
So, first off, shame on you ParagonWiki guys for not having all the shiney new stuff covered yet :P
Anyways, I've been going back and forth over getting the Cloud & Lightening trail aura since it came out, because Emps are a pain to farm I don't want to waste them. What I want to know is whether or not the aura is/can be set to appear only while flying. Because I don't want a cloud hanging around me at all times, only while flying. After all, I am "Capt. Stormrider" so it's only logical that I would literally ride a storm...
The off-beat space pirate...Capt. Stormrider (50+3 Elec/Storm Science Corruptor)
The mysterious Djinn...Emerald Dervish (50+1 DB/DA Magic Stalker)
The psychotic inventor...Dollmaster (50 Bot/FF Tech Mastermind)
Virtue Forever.