Hiro Ishikawa was the father of Keiko Ishikawa, later Keiko O'Brien.

If her first child, born in 2368, was male, Keiko wanted to name him after her father. Her husband, Miles O'Brien wanted to name the child after his father, Michael. Ultimately, as the baby was a girl, neither name was chosen. (TNG: "Disaster")

This character was only mentioned in dialogue.