Ishigami Village (founder)
Senku (adopted son)
Chapter 42 (Introduction)
As a middle age man, Byakuya grew his hair just the the nape of his neck and has a buzz-cut beard and mustache. His hair is blond and his eyes are brown, like his son.
Byakuya was a very supportive and caring father, who loved his son Senku. He went as far as selling his car to give Senku the materials he needed to become a genius in science. He was a caring person who was willing to work hard in order to give Senku a great future.
When Senku first showed signs of being interest in science, Byakuya did not hesitate to sell his car in order to give Senku the opportunity to explore his scientific interest. But unlike Senku, Byakuya was a lax and carefree man. He liked to talk about poetry and fairy tales and would get scolded by Senku because of it. Nonetheless, Senku influenced a lot of Byakuya's personality and behaviour. Although he initially gave up on his dream as an astronaut, he was once again motivated to become one when Senku tried to help him overcome his weakness of not being able to swim in clothes.
He was able to avoid the petrification on Earth as he went on a long term mission to outer-space after becoming an astronaut. After returning to a petrified Earth, he spear-headed a colony of survivors and founded a village in the hopes that it would aid his son in saving civilisation, Ishigami Village.
In Chapter 10, Byakuya is shown in a flashback of how he sold his car in order to give Senku the opportunity to explore his scientific curiosity. Byakuya is later shown in Chapter 42 in a flashback of Senku's memories, in which Byakuya wasn't able to become an astronaut because he couldn't swim in clothes. Senku, wanting to help his father, developed a suit with Taiju that used electric signals to forcibly move a person's body, and thus training them with motions. Although the suit didn't help much, it was enough to motivate Byakuya to learn how to swim on his own and became an astronaut. Just before Byakuya took off to space, he went in front of the announcer camera and swore to Senku that he'll bring back some space souvenir for Senku. It was then revealed that he returned to Earth after the mass-petrification of humans and founded Ishigami village.
Chapter 44, he was in the International Space Station.
Chapter 60 he left a time capsule disc for Senku, with the help of the 100 Stories.