39

39 is a "sister" of 42 and 35 mentioned by 35 during the chapter Technology.

Background
39 is part of a series of robots built by Ishinomori and sent away before he was arrested. It is implied that she's somewhere in the same city as 42 but her exact whereabouts and condition are unknown.

Personality
Details on 39's programmed personality are not known at this time.