|Stat spread is 36/40/39/12/28.
Olivia's job has been and always will be to Dance, but this build takes advantage of her stat spread to give her additional utility as a team debuffer. The weapon of choice here is Smoke Dagger+ with a Spd upgrade. This upgrade brings a devastating effect, which deals -6 Atk/Spd/Def/Res to target and foes within 2 spaces.
For her passives, Swift Sparrow 2 is taken to help her poor Atk stat and ensure that Windsweep 3/ Watersweep 3 activates. Her C-slot and S-slot remain Flexible to fit your team's needs. Field/combat buffs are solid options, or Savage Blow 3 and Poison Strike 3 can be used to add some chip damage to your debuffs.
The best special for this build is Aether. Since Olivia will likely only attack once or twice, and each will be a guaranteed single hit because of Windsweep, Aether is chosen to increase Arena score considerably, which is important due to her low BST. For other game modes, Aether can be still be taken or can be switched to Moonbow or another special.