Sonoka is the current leader of the Virus group, and has a particular focused interest in Lucia and Sumire.
She is a devoted follower of Aion (Lucif in the anime) and his quest to find the True World. She believes in what they are doing with hunting down shards, but gave her subordinates orders not to touch Lucia or Sumire.
She has blond hair that is often seen put up in a bun, and red eyes. She wears wire rim glasses, a black dress, and red high heels. In the manga she is mostly seen back at the Virus headquarters, watching how things unfold.
Sonoka makes her first appearance in Chapter 7, issuing orders to two unseen people (presumably Ruka and Guy) after watching the fight between Lucia and Sumire using her little compact mirror type object.
She is mentioned in Chapter 9 when Ruka asks her permission to make Sumire cry. At this time Ruka is addressing a small flying eye type creature, which is what Sonoka uses to spy on the events taking place in town.
We next see her in Chapter 11, watching Ruka and Guy on the roof (through the eye of the creature) as she implies that she plans to get rid of Ruka once she is no longer useful.
In Chapter 13 she outlines the first phase of their plan to find all the people with vision, in order to harvest shards. It's at this point that she sends Layla, Ruka and Guy out hunting for shards and threatens to kill them if they "touch" Lucia and Sumire. To illustrate this, she crushes her little spy eye creature (which is either replaced, or has great regenerative abilities because it is back to spying by the end of the chapter).
She is seen a few times in Chapter 14, but mostly just glimpses of her observing the events taking place.