I listened to it and it sounds like a hybrid of techno, industrial, and anime music. I don't know anything about the band. The only thing I could find on the internet about "Song of Saya" referenced a video game. Without any available information there's really little I could personally say about the music, for good or for bad. Without more information I'm not endorsing the music, nor am I condemning it, but I will tell you that you should listen to your mother. Especially if you're under 18.
On further research, I have discovered this article from Wikipedia. It doesn't look encouraging to me. link
*Saya no Uta (沙耶の唄?, lit. Saya's Song) is a visual novel by Nitroplus with horror elements.
Like Nitroplus' heavily Mythos-inspired Demonbane series, Saya no Uta's plot is somewhat Lovecraftian. Although direct references to the Cthulhu Mythos are minimal, the dark, eerie atmosphere is reminiscent of his works.
Many plotlines of Saya no Uta are similar to the manga Phoenix - Resurrection, specifically the life of Robita. At one point of the dialog, the main character explicitly references these similarities.
On February 24, 2009, the complete English 1.0 translation patch was released. The patch, while requiring a copy of the original game, translates the entire script in the game, allowing the fans who may not understand the Japanese language to enjoy the story as well. As of 7/09, this patch was no longer online, as JAST USA bought the rights.
A three-issue comic book based on Saya no Uta, called Song of Saya, has been produced by IDW Publishing. The issues were released from February though April 2011 .
As of July 2011, Jast USA has officially announced that Saya no Uta will be released in English.*
After reading this article I would have serious questions about the music as well as the videogame. If the storyline is based upon anything written by HP Lovecraft(who I am familiar with), I would avoid it like the plague.