This article contains spoilers for Golden Kamuy story. Please read at your own risk.
Olga is a small baby with a round face, light hair, and dark eyes. She would sometimes be covered by a blanket and on occasions would wear baby clothes when having her pictures taken by her father.
As Olga is just a baby, she has no known personality and presumably behaves as a normal baby would.
Olga was born to Kouichi Hasegawa, a Japanese photographer living in Russia and Fina, a Russian woman. One day, as Fina held Olga in her arms, Hasegawa returned from a photography session and greeted both his wife and daughter, asking if Olga had been good. They were joined by two men and a woman who had come to Hasegawa to learn Japanese. Over the course of several months, Hasegawa would hold Olga as he taught them his language and would take pictures of Olga with her mother. One of the guests, Zoya seemed more interested in Olga than her Japanese lessons.
Some time later, Hasegawa tells Fina to return to her family home and not to return until he comes for them. Heeding Hasegawa's words, Fina takes Olga and begins the trek past a group of Okhrana officers heading towards Hasegawa's store. When Fina finds a wanted poster of Wilk, she decides to return to the store out of concerns for her husband. They are ultimately caught in a gunfight between the revolutionaries and the Okhrana officers which led to them being pierced by a single bullet. As a result of the battle, Olga was killed and Fina left mortally wounded by the time Hasegawa found them. After revealing his true identity to Fina, Hasegawa takes Olga and holds her in his arms one last time. He then places both Olga and Fina in the bed at his store and lights the building on fire before walking away.
Sofia has always blamed herself for Olga's death, despite not knowing whose bullet had killed her. As such, she denies her own happiness as a woman and refuses to be with the man she loved out of fear and guilt that her life as a revolutionary would also get her family killed. Olga's father also became heavily affected by both the loss of his wife and daughter, which played a factor into him developing a twisted mind as well as a distrust towards the government.