Saeko Busujima (毒島冴子, Busujima Saeko) is a student at Fujimi High School, a member of the survivor group led by Takashi Komuro, and the daughter of Master Busujima. Before the apocalypse, she was in her third year and was also captain of the Kendo Club at Fujimi High School. In the group, Saeko is considered the most reliable of all fighters, and everyone can count on her combat skills to pull them through a tough spot if need be. Like Rei Miyamoto, Saeko is an athletic fighter and talented combat specialist whose forte is in melee attacks. She is one of the reasons why the protagonists have managed to survive as far as they have. At the beginning of the series, she uses a bokken wooden sword that she used to fight "Them" with, but she was later given a sword to fight "Them."
On the day that Fuse invaded, Saeko was mad at the rest of the crew. It was only a year after the zombie apocalypse, and Takashi had found a new girl named May. Saeko ran away and since then has been trying to make contact with the High School group but with no success.
She asks players to disable the jammers from the Fusions, so that she can make contact with Takashi. When she does, Takashi explains that May is his girlfriend because they were the last students left at Fujimi High School after the FusionFall.
Saeko asks the player to visit Takashi at Fujimi High School, where Takashi informs players of a Fusion Saeko running around the Sports Fields and asks them to defeat her, for which they will receive a Saeko Nano.