003 is the 7th chapter in the manga Ajin: Demi-Human, created by Gamon Sakurai.
The chapter starts with Kei groggily waking up from the events of chapter 6, questioning why he can't see anything. After learning that he is wearing a blindfold, Kei realizes that he has been captured by the government, and is laying face-up on an experiment table, completely covered in bandages with the number, 003 on his blindfold.
There is a brief cut to news reports informing the public that Kei had been captured in front of the police bureau, interviewing one of Kei's ex classmates. Tosaki questions the reason behind Sato's betrayal of Kei, but drops the matter almost immediately. Kei discovers that the researchers has severed his vocal chords, and after a brief conversation, they begin to "experiment" on Kei, sawing of his arm to compare to the one at the scene of Kei's first death, and cutting off his fingers to gauge his reaction to pain and "guesstimate" how many deaths he's had.
Suddenly though, scratches appear on the two sided mirror inside Kei's cell. After Tosaki consults with Izumi, she reveals that it is indeed Kei's IBM, at which point he wonders why he doesn't attack the researchers. A discussion ensues between everyone present at the other side of the glass, and when Tosaki asks what it's doing, Izumi says "It's looking at you, mister Tosaki".
Kei meanwhile begins to have an internal conflict within himself, Tanaka appearing before him as his more sadistic side. Tanaka says to him that the only reason Kei pretended to be on his high horse and look down on him was because he didn't know what it felt like, and that he needs to become who he really is. Just before he can kill the researcher however, Kei remembers the look Kai gave him at the river bank, and disperses his black ghost before any damage is done. Tanaka asks Kei why he didn't do it, and Kei responds by saying it would be a betrayal of Kai. Tanaka disappears after Kei is killed by the researcher, and experienced a moment of peace, but is snapped back to reality when the researchers return and say they must inflict as much pain as possible.