Raymond was a former colleague of Faust’s before the incident… of course he died shortly after becoming Judgment. Crow Kuruwaba was also “reportedly” in the medical field but he fell from grace much sooner than Faust did… and hasn’t exactly tried to redeem himself for his actions, which he claims are all for his research.
He tries to mock Faust to give in to his desires to “become the same” as Crow is… but Faust says he has a duty to save lives and will see to it that Crow pays for his crimes… assuming Faust can catch someone as evasive as Crow.
Fanny (a Nurse Assistant Faust knew some years prior) was rumored to be looking for Dr. Baldhead… though whether or not she knows Faust or if Faust was his original name to begin with is unknown.
Ky Kiske fought “Dr. Baldhead” in the original 2nd Sacred Order Martial Arts Selection Tournament (the first Guilty Gear)… so later when he encounters Faust periodically, he sees a similarity in Faust’s fighting stance and asks the question “Have we met before?” whenever they meet, though Faust never gives him a straight answer. A “substantiated” rumor has it that Dr. Faust assisted in Dizzy giving birth to Ky’s son, Sin… as much as that is implied… there’s no info to actually prove it (and it would certainly explain how Sin’s childhood was kept a secret if that were the case). Even so, it seems that in GGXrd, Ky is relieved to know that Faust has returned to his sane self.
Leo Whitefang makes an offhand joke to Faust about having caught a runaway doctor and having to return him to the royal hospital… it suggests he knows Faust is trying to redeem himself but is on the lam.
Faust isn’t the type to stay in one place for very long (something even Johnny of the Jellyfish gripes about as he had a hard time tracking him down for May’s sake), so anyone who knew about his past is either long gone or is still someone important that he is still trying to track down as is the case with Chronus of the Conclave.
Knowing now that Zato=ONE was responsible for his failure, Faust is struggling not to hold a grudge against the assassin and kill the man in revenge… while simultaneously trying to save Millia Rage from the same fate Zato had. Despite it all he holds a strange cordial relationship with Slayer…
Potemkin claims to “see though” Faust’s silly antics to the “core” of Faust’s combat style… though how much Potemkin truly knows is something he’s keeping to himself!