During the first Kage Summit, Mu and Seika accompanied the First Tsuchikage. Bringing the two tailed beasts to Iwagakure proved to be quite a challenge, however sealing them inside a human being was even harder. During the sealing of the Five Tailed Beast, the giant horse-looking beast went rampage, killing people left and right, until Seika fought against it. Seika manages to hurt the beast, and after sharing her apologies to it, the Five Tailed Beast agreed to be sealed only if her Jinchuriki would be Seika.
The First Tsuchikage created the Academy, which also allowed him to create teams of three to send on missions. Mu, Mito, and Seika were placed in the same team (at first, Mu was in a different team, however he managed to convince the Tsuchikage to let him be in the same team as his sister).
Three years later, Mu became the Second Tsuchikage. Mito and Seika moved in together after Mu moved into the Tsuchikage's home.
The next few years, Seika slowly started becoming like she was before her father died with the help of Mito, and the relationship between the two changed. They started dating when they were in their 40s.
When the twins were 51, Mu engaged into a battle with the Second Mizukage, and the battle ended with the two of them dying. It took Seika a while to move on, but having Mito by her side helped a lot.
When she was 57, one of her acquittances died during a mission, and her young child, Roshi, was left without a family. Mito and Seika took him in and raised him. The Third Tsuchikage told her to train the young boy because he was to become the next Jinchuriki for the Four Tailed Beast.
During the First War, Seika was dispatched to the battlefield, while Mito was allowed to stay back and take care of their adopted son. The following year, Roshi became a Jinchuriki, and the training became even more draining for the child.
Four years later, at 65, Seika died.