Saejima worked with Irene to convince Yanao Seijin that his mother Christie had personally recommended him for the use of the Animus "game", secretly a way to have him relieve the genetic memories of his ancestor, Edward Kenway in order to find the Observatory for the Templars.
After Seijin received an injury from his Animus session, he was sedated and taken to a personal room for himself. Here, Saejima greeted Seijin when he awoke, and informed him that they were under surveillance. Saejima declared himself to be Seijin's ally and asked him to help save his mother. Irene soon arrived and explained to Saejima his mother's condition: self-induced catatonia to impede Abstergo from using her to locate the Observatory.
As Seijin was forced once more into the Animus, Saejima told him that he would save both Seijin and his mother.