Chapter 42 (Introduction)
Byakuya Ishigami is Senku's father. He was an astronaut that was in space when the mass petrification on Earth's surface occurred.
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 is shown to have been a supportive parent to Senku. He went as far as selling his car to give Senku the material he needs to become a science genius. He's a caring person who's willing to work hard for the little motivations that his son gives him.
Byakuya was a caring father who loved his son Senku. 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 likes to talk in poetry and fairy tales and would get scolded by Senku because of it. Never the less, his actions is influence a lot by Senku. Despite giving up on being 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. He was able to avoid the petrification 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 create a village which was name after him. The 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 mind. Byakuya is later shown in Chapter 42 as a flashback to Senku's memories of how he wasn't able to become an astronaut because he couldn't swim. Senku, wanting to help his father, develop a suit with Taiju that uses electric signal to move a person's body. 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 takes off, he went in front of the announcer camera and swear to Senku that he'll bring back some space souvenir for Senku. It was then revealed that he return to Earth after the petrification and help develop the Ishigami village.
Chapter 44, he was in the International Space Station.