Kuroi Abe is the maternal grandfather of Shizuki Ryouko and father of Kuroi Nakase. Despite his old age he appears to be 27 years old. He has the formal education and abilities of a physician, but it has been over a century out of date since he last practised.
Having grown up in the population boom and wild technological advances following the Unification Wars, he has a tendency to nostalgically or melancholically refer to the past, which he often refers to with "back in my day". Regardless of or because of this, he is canny and wields his life experience with wit, either in avoiding family conflict or knowing just the right questions and vocal prods for a given situation.
A little bit shorter than average, he resembles his daughters strongly. He likes to maintain his hair combed and styled.
Born into the Kuroi Matriarchy, his choice of wife – Ryouko's grandmother – was strongly disapproved of and may have let to his estrangement from his branch of the Kuroi family. He nevertheless had two daughters, Nana and Nakase. The consequences of their respective Contracts, in combination with the MSY requirement that it be kept a secret from his wife, put a strain on the family, leading to Nana's eventual estrangement from the family and apparent disappearance. After the advent of the Contact War, Ryouko's grandmother deduced the true state of things and, feeling betrayed, left the family the join the military, though without filing a formal divorce.
Abe still pined after her, though, and after remaining on Earth briefly to stay with his recently born granddaughter Ryouko, eventually chose to follow his wife in to military, with the open goal of attempting a reconciliation.