|A meme build that ended up being viable somehow. The power held by Sonya with this is not to be triffled with as she can be both a player phase Mage AND an enemy phase one. The Owl Tome gives her a nice boost in her normal destructive power, adding a minimum of +2 to all of her stats with a single ally supporting her. The refinement can be either Speed or Resistance, which are both great solutions for Sonya.
Her Assist can be either Draw Back to safely retreat, or Reposition... but that depends mostly to you. Personally, I went for Draw Back.
Pairing her Owl Tome with a bond skill as an A slot, Sonya gains up to +7 depending on whether you use Atk/Spd Bond or Atk/Res Bond. Of course, Fury 3 is also viable as a budget solution and allows better synergy with her B slot options.
The B slot is Desperation as her doubling power is already high enough for the units she's intended to take on, but Vantage can be a solution as well depending on your playstyle.
The C slot is generally for Ploy skills as Sonya can run them rather well, but anything else can be used depending on your team composition.
The Sacred Seal could either be a second ploy like Atk Ploy 3 or Def Ploy 3... but there's also the option of Heavy Blade 3, allowing quicker special charge in order to eliminate her opponents more easily, as her high attack stat would allow her to make good use of it. Distant Defense is also a viable option if you prefer focusing on Enemy Phase rather than Player Phase.
As a special, Iceberg is a very good option for Sonya as it makes good use of her resistance and is rather quick to charge. Glacies can be used as well if you don't mind the 4 cooldown. You can still run Moonbow or Luna, but those wouldn't be as effective as Iceberg without Dark Excalibur.
In terms of ally support, there are two types of options you can go with: either a strong red unit that needs to have its weaknesses covered by Sonya - so being protected from blue threats like Reinhardt, Micaiah or Effie... or a blue unit capable of protecting Sonya from red units that could easily dispose of her.