Seido Hishigata

Seido Hishigata (菱形 青銅, Hishigata Seidō) is the father of Sou and Tokiko. He is the director of the only hospital on Hitogashima, the Hishikata Clinic.

Appearance
Seido is an adult man with short gray hair. He also wears glasses.

3rd Loop
At Hishigata Clinic, Seido is with a shadow in a wheelchair. He sees the red light in the sky and comments that Heine had recovered by consuming thousands of humans.

4th Loop
Seido calls Negoro and tells her to use the policeman's, Tadashi Miura's, body as today's food at 9 o'clock.

7rd Loop
Shinpei's group arrives at the hospital to see all items and furniture erased and traces of a fight that leads them to the basement morgue. There they continue through a hallway that leads to Hiruko Cave, and on the way they find Seido being choked by his wife, Chitose. Ushio stops Chitose and severs their connection with Heine. As Seido isn't breathing, Tokiko and then Sou, give him first aid and manage to save him. Seeing that they had gotten to this point, Seido realizes that's why Heine wanted to kill him: she was afraid he would tell them everything. He orders Tokiko to kill them, so he could regain Heine's trust, but Tokiko refuses, acknowledging that the shadows betrayed them. Enraged, Seido manages to take the gun from Sou and shoots Tokiko. He turns to Ushio, but Tokiko then stops him, revealing she was actually Shadow Mio. Seido refuses to talk, Shadow Mio attempts to scan him but learns that he is immune. Negoro then shows up with Ushio's body and gives Seido a message from Shide, thanking the Hishigata family for all their help, but this is the end.

Realizing he is immune and can't achieve his goal, Seido decides to talk. He reveals that Heine wants to return to her world, which only shadows can reach and he was supposed to join her with his wife Chitose, Tokiko and Sou. Chitose calls him an idiot, but thanks him for saving her, and tells him he can still do the right thing. Seido calls Tokiko to dig up a safe he had given her, containing a list of patients who had died and had been fed to Heine. Including Shinpei's parents. Seido also shows a photo, revealing that Shide is Heine's guardian and the first child she gave birth to: Shidehiko Hishigata, the founder of the Hishigata Clinic, as well as its first director.

Seido reveals Chitose's ashes to Sou, confessing that he couldn't give her body to Heine for food. He reveals that she died from heart failure on January 3rd, 2013. Sou realizes that was days before the supposed surgery where they found a donor. Seido reveals that Hishigata had been serving the shadows for over 300 years and there has always been only one successor. He believed it would be too much for Sou to bear and that's why he chose his sister as successor.

Etymology

 * The name Seido means "bronze" (青銅).
 * Seido's surname Hishigata means "Rhombus, diamond shape" (菱形).