The role of the Star Singer is basically to shut herself inside the Crescent Chronicle, and continue singing Chronicle Key without any pause to keep active the seal that maintains Mir sleeping. This has to be done continuously for at least twelve hours in order for the seal to be at maximum strength at all times, since otherwise, the strength of the seal would weaken and gradually it would allow Mir to fight against it.
The Star Singers are invariably Pureblooded β-type Reyvateils, due to having anatomical and strength specifications that Third Generations can't reach. They are created in the city of Platina, raised under a rigorous training regime to bring out the power of their songs, and taught all sorts of things about the functioning of the Tower and other matters. Then, when they turn eight years old (two mere years after their birth) they are sent to the Tail of Reminiscence in company of the general populace of Platina and Em Pheyna to undergo a ceremony that will bestow upon them the title of Star Singer. Then, they are sent to Em Pheyna and the Crescent Chronicle, upon which they must start singing. 
However, and unlike what Misha has led us to believe, Star Singers only must sing for around 30 years. Once this time expires, they will be released from their responsibilities, and will be allowed to live however they wish in the city of Platina, while receiving full support from the government. However, a little before that time a new Star Singer will be created and trained to replace her, thus reinitiating the cycle. This measure was put in place because some of the first Star Singers got killed in accidents, and because the power they exhibit when singing Chronicle Key begins decaying after that span of time, so in order to keep Mir's seal functional, the singer has to be replaced. 
Currently, the only known Star Singers are Misha Arsellec Lune, and the founder of the Star Singer lineage, Lune. Tastiella de Lu also was known as an Star Singer when she was alive, but given she wasn't a Reyvateil, and she gave her life to create the Crescent Chronicle, the definition given in this article can't be applied to her.
- Although Misha states in the game that she is the 31th Lune, this is chronologically impossible: given the time the Star Singers keep singing is only for 30 years, and only 349 years have passed since Lune sealed Mir away until the events depicted in Ar tonelico: Melody of Elemia, only 11 Star Singers could have existed in that span of time. This is, of course, unless we count the Teru Star Singers, but neither the game or outside material have said anything about them.
- It is known that the name of the Star Singer role comes from a facility called the Star Gazer located in the Soreil Migratory Ship. Shurelia sneaked on it once, and asked Delta and Casty to take her to said place. She was marveled upon hearing what the facility was used for and the meanings for its name, so she pretty much copied the name for the Star Singer lineage from it. She also stated she had intentions to make a similar facility in the First Tower of Ar tonelico, so most likely the Observatory was also one of her creations.
- ↑ Ar tonelico Official Materials Collection: World Section & History Sections
- ↑ Ar tonelico Official Site - Ar Portal: Toukousphere Issue #17