His official designation is, Servant AUX Voroid "K6-X4". It is a Servant auxiliary high-performance robot meant for combat and navigation assistance. A trusted partner of X Alter's ever since she could remember, who she nicknamed "Black Knight-kun".
His character is bad and so is his tongue. He's not fit to appear in public. He completely looks down on humans, and will even ignore orders, but he is loyal to the end to X Alter alone.
In his head, minute Alternium crystals are buried, which are synchronized with X Alter. By the way, its body which is reminiscent of an ancient helm is the repurposed head of a rampaging mechanical giant which once turned an entire planet into scorched earth.
"Is that so... poor you.There are people who have been treated so cruelly too..."