After becoming a Spirit, Chihiro returned to her eighteen year old self, as did Haku.
Haku and Chihiro got married as soon as she was settled in.
Sen grew up happily surrounded by the Spirits coming and and out of the bathhouse. She eventually forgot that she had a life other than being a Spirit. After about a month she did odd jobs for the workers of the bathhouse when she was old enough, she got to work in the bathhouse taking Chihiro's place. She also became Boh's best friend
Yubaba was annoyed that she had to have a free ward in the bathhouse, but soon Sen became the little runner around the house, Yubaba forgot what it was like not to have her there.
Boh didn't like Sen for a while, since she took up all of Chihiro's time, but when Sen agreed to play with him for hours on end, he wanted her with him forever.
Mangetsu and Miyaki ended up with Soren in the Wastes.
Chihiro had another child after she and Haku were married. It was a boy.
Chihiro's body was found in the Kohaku River about a day after she joined the Spirit World. It was pronounced as a suicide, since her daughter had died the day she had apparently drowned herself. Her parents thought it was because she lost Nagiori and Sen. They had a funeral for both mother and daughter. They were saddened by the loss until Chihiro and Sen visited them in a dream and told them both that they were happy now. "With Daddy" Sen said. They thought she meant Nagiori, even though she never knew him.
Chihiro was so happy that she was with Haku and her daughter that she never missed her life, until the day that she saw her parents pass through the Spirit World. Realizing how much she missed them, and how hard it was for them to lose her, she broke down crying. Haku held her and comforted her for a week while she mourned for them.