He appears briefly when Cyan Pile decides to leave the blue legion and join Nega Nebulus, instead of using the Judgement Blow on him, he decides to spare his life for unknown reasons.
In volumes 6 and 11, he features as the one to host all the 6 Kings of Pure Colour Conferences via his two Lieutenants, Cobalt Blade and Manganese Blade. Furthermore, he later becomes the "Judge" who determines whether a bounty will be put on Silver Crow or not after he becomes infected with the Disaster and is given a time limit of one week to purify himself of it.
Simply put, Blue Knight is as his name describes him as: a knight. His avatar is prodominately colored in various shades of blue, with a few yellow crystals on certain spots of his armor. He also has a helmet with curved horns and an equally blue cape, completing his appearance as a head knight of sorts.
Blue Knight's abilities are mainly unknown, but it's quite obvious that he has high quality swordsmanship. His strength is also further proven in his level 9 status and his titles such as "Vanquisher" and "Legend Slayer". His sword is one of the seven Arcs, the First Star of the Dipper Alpha, Great sword The Impulse. He is respected enough to be chosen as the one to judge whether or not Silver Crow should be uninstalled after he equips the Disaster Armor.
In vol 12, his abilities are listed as Unlimited Driving Force and Pain Killer, suggesting that he possesses techniques geared towards direct confrontation of his opponent no matter how powerful it may be.