Corse Party D2: Depths of Despair
Seiko arrives to the class reunion that Yui set up in classroom 2-9 at Kisaragi Academy along with the others. While she notices that Ayumi seems to be feeling down, Naomi tells her to socialize with the others to speak with Ayumi in private. After Yui suggests telling ghost stories, Seiko gets excited and teases Ayumi for not being interested.
Seiko makes a cameo in the Mended Soul ending, where she tells a ghost story involving a "wet bread monster" and Miyu Shinohara.
Corse Party D2: Fatal Operation
Seiko comes to Divine Blessings Hospital to meet Naomi since she works in there, but is stopped by the staff. She writes a text message to Naomi saying to let her in. While waiting for Naomi she meets Kensuke Kurosaki who is looking for his friend that is a patient here, Yuuya Kizami. Naomi comes and they chat, after that Kensuke leaves.
While Seiko and Naomi are both inside the nurses office, an earthquake began and they both pass out. They wake up to find the hospital abandoned and looking different. They find out that the are now stuck in a different dimension. They both set out to look for an exit and on their journey find out that people were sent here before them and the dead ones rise up as zombies. Inside one of the offices they read a newspaper clipping and Naomi snaps, yelling at Seiko, which makes her sad, so she leaves her alone.
30 minutes before Naho, Naomi, Haruna, and Seiko enter the basement of Divine Blessing Hospital, Seiko encounters Yuuya, who was stuck climbing out of a pit. He joins her and they both find a rusty key held by a headless corpse. The key unlocks an operation room, where Seiko is attacked by her zombified mother. After Yuuya cuts the reanimated corpse off of Seiko, he reveals his intention to kill her. Seiko flees out of the room and escapes from Yuuya, finding the key to Machi's room with the help of a spirit. She then hurries towards Machi's room, where she is suddenly attacked by Machi's ghost. She then dashes towards the same pit Yuuya was hanging on to earlier in a failed attempt to escape Yuuya and Machi. She slips and falls into the pit in shock when Machi appears behind her.
Seiko's appearance in this chapter will depend on the player's choices in the first part of the chapter:
If the player decides to skip looking for information, Seiko is knocked unconscious by the fall and Machi claims her body. At the end of the game, Seiko is shown wearing a patient outfit similar to the one worn by Machi. Because her spirit was left behind at Divine Blessing Hospital, she talks with sudden breaks in her words. Seiko's spirit appears before Naomi after locking her in the nurse office in the real world. Saying that they will be together forever, she crushes Naomi for not realizing that Machi had possessed Seiko's body.
If the player decided to discover the truth about Machi, Seiko will survive the fall and will learn the truth about her mother from Machi. She pities Machi and tries to offer her help in leaving the hospital, which angers Machi. Machi tries to kill Seiko instead but is stopped by the spirit of Sayaka - Seiko's mother. Seiko runs out of the room and bumps into Naomi and the others. They all proceed to appease Doctor Fuyu Hirata and escape from the hospital. In the epilogue Seiko asks out Naomi for a date and Naomi accepts.