Olivia

Semi-budget dancer, currently a 4* +6 unit. (stats shown are base, not factoring in weapon, Fury, or seals.)

With Ruby Sword+, Fury, and Moonbow at her disposal, Olivia can step out from behind her team and take out the likes of Hector and B!Ike, allowing her to not only serve as a dancer but as a fighter in her own right. Ruby Sword+ and Fury 3 are required to ORKO a +Def Hector in the player phase, but with less merges, neutral IVs, and/or only a vanilla Ruby Sword, it can still be possible to score KOs on Hectors if you can bait him into attacking first (beware of the likes of Bonfire being charged up in these cases).
In theory, Brave Ike tells a similar story, requiring about the same investment as with the +Def Hector to ORKO Ike with equal ease, providing he doesn't have Ignis ready to go. In general, opposing specials are the main factor to be wary of.

Beyond all this math and theorycrafting, Olivia's main role is just to sit behind her allies and let them borrow her turns, so there's no need to do much else regarding her offensive presence. The anti-Hector, anti-green route is a fine option when considering the fact that Olivia likely takes up the red slot on your team, and may occasionally be the only one with color advantage against a particularly annoying green unit.

*Stats shown with Weapon and Fury*

Weapon: Wo Dao+
Assist: Dance
Special: Moonbow
A-Slot: Fury
B-Slot: Escape Route / Wrath / Swordbreaker / Axebreaker
C-Slot: Hone / Spur / Drive
Sacred Seal: HP +3 / Speed +1 / Attack +1

Single shot rifle build, +Spd, +Atk / -Res.

With this build, Olivia is capable of utilising her lack of bulk without Ruby Sword along with Fury and her speed to safetly reach Escape Route range whilst dishing out a large amount of punishment in the process.

This build is actually specifically oriented towards a more supportive playstyle due to the fact that she cannot sustain very much damage, even from greens, mainly due to her low HP and average defenses.
Olivia will mainly be focused around abusing her Dance until she is needed in the fight, then using her high speed and her Wo Dao!Moonbow combo to severely wound or kill her target through a trade and put herself into Escape Route range in order to further abuse her Dance.

On the otherhand, Swordbreaker or Axebreaker can be ran in order to provide Olivia will more initial firepower rather than delayed supportive potential, and even Wrath can be taken into account if Escape Route support is not necessary and you're looking to further her role as a one-shot wonder.

As a final note, due to the nature of Escape Route, a Spur/Drive skill (preferably for Attack or Speed) can also be taken to maximise it's potential.

If QP cannot be used on another unit of your team, Olivia can also utilise it in order to bait and proc Moonbow regardless of her speed match-up against the enemy.

Taking advantage of Olivia's pretty good stats already, this set allows for her to tank a wide variety of hits, which opens up so many more options in game, while also turning her in to a reliable Hector counter with moonbow and a powerful red offensive presence that isn't locked in to her triangle. This set provides all of that on top of dance, making Olivia one of the best units in the game (in my opinion).