When they were just children, Vincent, Ren and Selina lived together, running amok and helping each other survive the harsh conditions of the Ryuuga Ghettos'.
Vincent secretly liked Selina, however she had feelings for Ren. This drove a feeling of inadequacy into Vincent, with him constantly feeling the need to prove himself - sparking an intense rivalry to become the strongest of the three.

When she turned 10, Selina's powers developed - becoming a member of the Lancer class.

Now having a new found confidence, Selina confessed her feelings to Ren, who by that time had become twisted and obsessed with his own abilities…not only rejecting her feelings for him, but refusing to acknowledge her all together.
This crushed Selina, and she left the Ghetto's - leaving only a letter behind to say goodbye.

Years later, Selina makes an appearance on the battlefield…now working under the Nexus banner by the name of Sonic!

Sonic is hot tempered and quick to jump into a fight, however be careful not to confuse her eagerness to fight for being too rash…for she is extremely intelligent, and utilizes her brilliant mind, her hot blooded attitude and her instincts flawlessly.
This makes her a perfect weapon and a threat to any members of GRAVE.

Powers & Abilities:
Despite being a Lancer Meister, Sonic now has a special ability to expand and contract her spiritual energy at an extremely high frequency. 
This vibration of energy, super-heats the air around Sonic for a split second, before emitting a massive clap of thunder from her body. 
The thunder varies in destructive capabilities, acting as something of a Sonic-boom and melting the ground beneath her as, well as anything within radius of her spiritual pressure of a few inches.

Sonic is labelled as a member of the "Forgotten"- a small group of test subjects who were experimented on by the same scientist responsible for the Mardock Trials and Kyo's creation.