His official designation is Servant AUX Voroid "K6-X4." He is a Servant auxiliary high-performance robot designed for combat and navigation assistance. A trusted partner of X Alter's for as long as she can remember, she nicknamed him "Black Knight-kun."
His character is mean and so is his tongue. He's not fit to appear in public. He completely looks down on humans and ignores orders as a matter of course, but he is loyal to the end to X Alter alone.
Minute Alternium crystals, synchronized with X Alter, are buried in his head. By the way, his body, which is reminiscent of an ancient helm, appears to be the repurposed head of a rampaging mechanical giant that once turned an entire planet into scorched earth.
"Is that so... poor you. There are some very cruel people out there..."