Total Recommendations: 2
While Shakugan no Shana is less serious than Ga-rei Zero, they both deal with the concept of keeping balance to the world by eliminating the beings that throw it off. In both, there are instances where personal feelings get in the way of duty and responsibility.
Both series have strong, skilled female fighters. The art style is very similar, with a noted similarity mainly in the clothing design of Princess Alita (the main protagonist). Like Saber, Alita is also (to some extent) king (since she's the only ruler of her country).