Theresa Cassidy

Theresa Rourke (Alias)

Sean Cassidy (Paternal Half Brother)

The Initiative (Former Member)

X-Force (Former Member)

## Background

### **1986 - 2005: Theresa Cassidy**

Theresa Maeve Rourke Cassidy is the mutant half-sister of Sean Cassidy, making her the second heir to Cassidy Keep. She is the second daughter of Liam Cassidy with his second wife, Maeve Rourke. Having already lost his first wife, Liam never planned on remarrying but met Maeve & immediately fell for her.

Due to the age difference between her & Sean, they weren't around each other a lot but Sean looked out for her whenever he came home. Theresa & her mother regularly visited her relatives in Armagh in Northern Ireland. While she was there, Maeve, an innocent bystander, was killed in a terrorist bombing along with a number of other people. No trace of Maeve was found by the authorities & Maeve's relatives took in Theresa until Sean arrived later that day. Now a second time widow, Liam became a recluse & focused all his time on his daughter.

When Sean confessed that he had mutant powers to his father, Liam suspected that Theresa might develop similar powers as she grew older.  At the age of fifteen, Theresa's sonic powers emerged & her father did his best to keep it a secret from everyone, including her brother who was going through a rough time in his life. For the next three years, Liam helped Theresa get control of her powers & had her take combat lessons as there was many people who hated mutants in the world.

After Theresa turned nineteen, she told her father that she wished to attend college in the states. It wasn't a complete lie but she had some ulterior motives as she had heard of the superhero team X-Men & was set on meeting them. Her arrival was brought as shock when her brother revealed himself as the superhero Banshee. The two were joyfully reunited, having not spent much time together in the last couple of years. After explaining to her father, he allowed her to divide her time between Cassidy Keep & the X-Mansion.

### **2005 - 2007: Siryn**

Instead of joining the X-Men as most had assumed, Theresa joined the newly formed & proactive X-Force. Though one of the youngest on the team, Cable frequently allowed Theresa to lead some missions, remarking she had an affinity for leadership.

As a member of X-Force, her teammate Warpath developed a romantic interest in her. Her brother did not appreciate this as Warpath had kidnapped him years ago when he was seeking revenge on the X-Men. Though things were solved between then, Sean still held some resentment for the mutant. However, Siryn began an on-going flirtation with the mercenary Deadpool. Again, her brother warned Siryn about her romantic choices, stating that Deadpool was a madman & a murderer. But she found herself quite taken with him, even looking past his horrific appearance. Due to this kindness, Deadpool became infatuated with Siryn to the point of obsession & often sat outside her window as she slept in the X-Mansion.

Over time, Siryn became the voice of reason in Deadpool's ear, attempting to sway him to the side of good. She assisted him in some of his missions but in the end, Siryn became overwhelmed with balancing her duties with X-Force & the demands of Deadpool's somewhat faulty sanity. They eventually parted ways & Siryn began focusing more on her X-Force responsibilities secured.

Though confronted varied adversaries during her time in X-Force, nothing prepared her to confront her more down to earth problems. One major issue of hers was alcoholism, an problem she had struggled with from a young age, even during her time at St. Elizabeth's. Warpath helped her to cope with her drinking problem & she began leading a sober lifestyle, while also starting a relationship with James.

During a clash with another team, Theresa's vocal cords were severely damaged when Feral slashed her throat, causing her to lose her voice as well as her powers. Taking a leave of absence from the team, Theresa adjusted slowly to life without her powers & began living on Muir Island with Moira MacTaggert. Theresa soon encountered Deadpool who managed to heal her with a blood transfusion of Wolverine's own healing blood. Moira was upset with Deadpool for doing this without consulting her but Theresa believed Deadpool made the right choice. However, she chose to remain on the island instead of leaving with Deadpool.

## Romantic Relationships

* Wade Wilson: "Boyfriend" (2005 - 2006)
* James Proudstar: Boyfriend (2006 - 2007)
* Jason Madrox: Boyfriend (2010 - )

## Powers & Abilities

* **Mutant Physiology:** Theresa possess acoustikinesis, the ability to create various sonic effects through the combined action of her vocal cords & limited psionic powers.
	+ ***Sonic Scream*:** Siryn can cause her vocal cords to vibrate over a wide range of sonic frequencies & produce a volume of sound.
	+ ***Flight*:** Siryn can use the sonic vibrations of her scream as a carrier wave.
	+ ***Sonic Lance*:** By focusing her sonic vibrations while screaming into an intense beam. This is used as a sort of "battering ram" that can stun or even destroy most solid objects.
	+ ***Sonar***: She can use her sonic powers as a form of sonar. By sending out a precise, pure note & listening to the returning, altered wavefront of the note, she can evaluate her surroundings in total darkness.
	+ ***Sonic Null Field***: She can project a field of silence in an area making no sound reach outside the area or no sound outside the area in.
	+ ***Sonic Amplification*:** She can amplify sound carrier waves allowing her to hear conversations or noises from far off.
	+ ***Sonic Shield***: She can tighten sound waves around herself or others near her, making a barrier against outside attack.
	+ ***Vocal Disorientation***: The ability to change someone’s balance, by affecting their equilibrium using her sonic scream.
	+ ***Vocal Trance***: The ability to subtly influence peoples subconscious mind by changing the tones & vibrations of her voice using sonics, the effects tend towards blatant hypnosis. At times she's been even capable of calming down an enraged Hulk (when his rage is not so intense).
	+ ***Vocal Unconsciousness***: The ability to affect the fluid in someone’s ear causing the person to go unconscious.
	+ ***Siren's Song***: The ability to influence human beings with a certain pitch of her voice, causing them to fall in love with her.
	+ ***Sound Immunity***: Siryn's hearing & equilibrium are unaffected by the effects of her scream & similar abilities.
	+ ***Superhuman Vocal Stamina***: Her vocal cords are tremendously strong, so that she can produce sonic effects through screaming constantly for hours at a time without noticeably tiring or injuring her vocal apparatus. Siryn's vocal cords & the interiors of her throat & mouth are also superhumanly tough, so that the intense pressures & constrictions that she produces do not cause her any injury.
	+ ***Sonic Scream***: Siryn can cause her vocal cords to vibrate over a wide range of sonic frequencies & produce a volume of sound ranging up to at least 140 decibels. Siryn has thus the ability to shatter solid objects with a sonic scream. This ability is most likely augmented with her ability to wield mythological Banshee cries which were demonstrated as being louder than her own sonic scream.

### Weaknesses

* **Power Strain:** Her vocal cords are susceptible to injury from excessive strain in using sonic powers. She has also survived major injuries to her throat at the cost of her sonic powers temporarily.
* **Alcoholism:** She is a recovering alcoholic.

### Ratings

* **Intelligence:** Unknown
* **Strength:** Unknown
* **Speed:** Unknown
* **Occult:** Unknown
* **Weapons:** Unknown
* **Energy Projection:** Unknown
* **Strategy:** Unknown
* **Fighting Ability:** Unknown

## Trivia

* Since she can't drink alcohol, she pours water into wine bottles so that she can pretend it is wine. She also does this to test if God is on her side. She says if Jesus loves her that he'll turn the water into wine.
* Her song causes her victims to fall in love with her, regardless of their gender or sexual orientation.
* At times, she's been capable of calming down an enraged Hulk (when his rage is not so intense).
* Jason Madrox is one of James Madrox's clones.

## Notes

* The original character of Siryn belongs to the Marvel Universe.
* In the comics, she is the daughter of Sean Cassidy.