Sergei, also known as "D," is Ajo's right-hand man. (Not to be confused with Assi, Ajo's personal secretary) Sergei seems to be a cyborg product of Ajo's work: he is human, but with artificial enhancements. Sergei prefers to keep his own agenda on certain matters; he frequently ignores protocol and performs his own investigations, much to Ajo's irritation. One unique aspect of Sergei is the pink, sublimating gel he apparently ingests as part of the operation of his prostheses. A waste product of the gel provides Sergei with a rather odd weapon; he can spit small marble-like solids with enough force to cause injuries.
Sergei heads the team sending the PPOR units on missions in Tokyo; even though Ajo persists that Dr. Mima's only surviving relative, Key, is of no importance since she could *obviously* have nothing to do with his poor "sons" getting destroyed, D is not convinced. (Ajo rejects the notion that Key is a robot, citing his rationale that robots cannot possibly have free will.) Sergei comes close to Key via the PPOR units twice, but each time Key's fugue and resulting powerbox feedback knock the PPORs out of commission. When Key's moment of extra-human, extra-robot lucid awareness arrives in episode four...BOOM!
Sergei is perhaps even more ruthless than Ajo. When confronted by the unarmed followers of
Janome's church, he guns them down with no more trepidation than if they were sheep. However,
Ajo himself delivers what is possibly the most interesting remark concerning Sergei. After the
failed assault on the Golden Serpent Association and his argument with Tomoyo, Ajo says to him,
"How does it feel to be beaten by your younger sister?"