(written from a Production point of view)
Takashi Kimura was a character mentioned in a part of a biography of Hoshi Sato that was prepared by Mike Sussman for "In a Mirror, Darkly, Part II". Only the first part of the biography made it on screen, stranding Kimura outside of canon.
According to the graphic, he was Sato's husband. After Hoshi Sato and her family were ordered executed on Tarsus IV on the orders of governor Kodos in 2246, she was buried with Kimura in Kyoto, Japan. The graphic does not make it explicit that Kimura was among those killed on Tarsus.