Lene, Yearning Dancer
Copy pasta from Olivia. Lene is slightly faster but a little more physically squishy.
Dancers/Singers are the ultimate support units in my opinion. They can give buffs with their C slot and Sacred Seal slot; counter any color their team has trouble with (besides PA!Olivia since she is colorless); and most importantly, Dance and Sing their teammates to massacre the rest of the enemy team, to retreat, or to undo a minor mistake.
As support units, a bad nature will not impact Dancers/Singers as negatively as it will affect combat units since their primary job is to Assist their allies rather than fight. Unless a specific nature is absolutely needed to counter a specific threat, natures are not too important.
Level 40 stats:
HP: 32/35/39
Atk: 24/28/31
Spd: 32/35/38
Def: 20/23/27
Res: 24/28/31
Total: 148~150
Default skills:
Weapon: Safeguard+
Assist: Dance
Special: [none]
Passive A: [none]
Passive B: Firestorm Dance 2
Passive C: Sword Valor 3
Ruby Sword:
General use, Arena offense, Arena Assault
Triangle Adept:
General use, Arena offense, Arena Assault
Player Phase Offense:
General use