Gaignun Kukai Jr. or "Little Master" as he is called by his friends is the commander of the ship Durandal, and with Gaignun Kukai Snr.
is a leader of the Kukai Foundation.
The following description contains plot spoilers
Jr.'s true name and origin is Rubedo, a Variant URTV (U-DO Retro Virus biological weapon) Unit #666. He has the mutated ability to control the development of his body cells, and for story reasons maintains a youthful form. For the sake of public perception towards the Kukai Foundation, Jr. is made out to be Gaignun Snr.'s adopted son, but in fact they are close to the same age and biologically more like brothers.
Jr. is a callback to the character of Billy Lee Black
, sharing the design characteristics of youth and wielding multiple guns.