Siryn (born Theresa Maeve Rourke Cassidy) is a mutant with the ability to produce a very loud, high pitched scream.
Siryn is seen as one of Storm's students at the Museum.
She, along with other students, attended Professor X's funeral.
When the X-Mansion re-opens, she is seen giving Storm a hug before returning inside.
- Acoustikinesis - Siryn has the ability to scream at sonic levels. It was able to disorient the entire school.
- Professor X - Mentor & Teacher
- Wolverine - Mentor & Teacher
- Storm † - Mentor & Teacher
- Jean Grey † - Mentor & Teacher
- Cyclops † - Mentor & Teacher
- Shadowcat - Classmate & Roommate
- Iceman † - Classmate
- Rogue - Classmate
- Colossus † - Classmate
- Jubilee - Classmate
- Cypher - Classmate
- Hellion - Classmate
- Jones - Classmate
- Artie Maddicks - Classmate
- William Stryker † - Enemy
- In the comics, Siryn is Banshee's daughter. However, Banshee in the Fox X-Universe is supposed to have died before 1973, making it impossible for the film version to be his daughter, although it could be possible she may be related through extended family.