Background
Tsukiko is the mother of Kiriko and Kai Masaki, and a distant relative of Tenchi's.
Biography
Tsukiko was born and raised in Masaki Village, among the other descendants of Yosho and his first wife, Kasumi. She was apparently a contemporary of Nobuyuki's, having witnessed how Kiyone treated Nobuyuki when they first met. At some point, she met and fell in love with a man, and after marrying, they had a single daughter named Kiriko. Shortly thereafter, Tsukiko's husband died. A few years later, Tsukiko entered a relationship with another man, and she became pregnant and gave birth to a son named Kai. However, for unknown reasons, Tsukiko and Kai's father's relationship deteriorated, and they remained together only for the sake of Kai. In the GXP novels, Kiriko once mentions asking Kai's father what happened, but he was kept silent by Tsukiko.
Tsukiko often took Kai to visit his distant cousin, Tenchi, as they were relatively close in age, and became playmates. In time, Kai made a new friend, Seina Yamada, who also became a close friend of Tenchi's. One day, while being visited by Seina's parents, they broke out into tears about how happy they were that Kai hadn't been driven off by Seina's bad luck. Unknown to them, young Kiriko was watching from the door.
When Kiyone, Tenchi's mother, died, Tsukiko took Kiriko to the funeral, which was limited only to blood relatives.
As Seina grew older, Tsukiko found herself drawn to him more and more. While Tsukiko and other of their relatives were getting ready for Rea's wedding, some of her cousins began to pester her about making a move on Seina, where Tsukiko ranted how Seina was still too young for her to start a relationship with him.