A bystanders placeholder for subthread hopping would be awesome sauce. You know there's nosey characters that would need to be pulled away.
Ether attacks have different elements. The ones used in the game are Ice, Fire, Thunder, and Aura. Aura would probably be closest to 'spirit' based attacks. Each element has three different eithers. 'Veil' is defensive, which is basically a sheild to protect against attacks in that element. 'Sword' adds the elemental ability to other non-elemental attacks. 'Burst' is an attack on it's own. Other things she can do include healing others, speeding up and slowing down attack times, and strengthening and weakening attacks and defenses of friends and enemies.
There's a good reference here. Under 'Type', it'll say 'Ether'. I'm not going with 'Equipped' or 'Mastered' because she might not have the equipment here in Marina, and the other is just too tricky to bring into an RPG like this because I'd have to take into account leveling up and playing time. Look for anything that has 'Aura' either in the name or the description. Those translate to spiritual spells that would most likely affect Xellos in some way.
MOMO's a really good support character. She's best for enhancing other people's attacks with either status effects, bonus attack points, or boosting up their speed, and for healing and reviving them when they get hurt or knocked out.