Kaito

カイト (黒い騎士), The Dark Knight

Prince of Forland, Kaito is Alita's older brother and eight years her senior. She speaks of him fondly, bragging of his swordsmanship as well as his kindness. Prince Kaito left the country to hold peace talks with Forland's western neighbor, the kingdom of Grandel, but no one has heard from him since.

When he comes back, it is revealed that he is the man clad in a heavy, dark-colored set of armor that accompanies Cecilia.

(Source: Wikipedia)