Mio Kofune

Mio Kofune (小舟澪, Kofune Mio) is Ushio's younger sister and a first-year high school student. She is good at sports, belongs to the swimming club, and has tanned skin. Despite the death of her older sister, she has a healthy side, such as her cheerful attitude toward Shinpei when he returns home.

Appearance
Mio is a young girl with medium long black hair and blue eyes. She also has a tanned skin.

Plot
After two years away, Shinpei Ajiro returns to Hitogashima to attend his childhood friend Ushio's funeral. Stepping on the island, Mio welcomes him and they head towards the funeral while chatting about various subjects.

The next day, Shinpei and Mio work at Kofune's dinner. The police officer, Tetsu comes and explains that the whole Kobayakawa family had vanished. Hearing that, Mio runs away and Shinpei follows her. After catching up to her, Mio explains that Shiori said she saw a girl looking like her about a week before the incident with Ushio. An old hunter, Ginjiro Nezu, tells them that's a shadow and those afflicted by shadow sickness, see their shadow and then get killed by it. The shadow then acts as the killed person and kills the remaining family. It used to be quite common sickness before the war and those afflicted went to Hito shrine for cleansing. Mio then states she saw Ushio's shadow along with Ushio, three days before Ushio died. Shinpei then decide they go to the shrine to learn more about the shadows. However, the shrine is closed at the moment and Mio sees Shiori in the forest and they run after her. They are unable to find Shiori, but hear a gunshot and following the sound, they see the woman with glasses bleeding from a gunshot. Mio heads to get help and the woman tries to tell Shinpei something, but get shot in the head. Shinpei then sees Mio holding a gun and holding the Mio that was with him as hostage. The other Mio then shoots Mio and Shinpei.

On his third time stepping on Hitogashima, Shinpei manages to stop Mio from falling in the water, but he ends up falling in it and she jumps to save him. That evening, he records the Shadow Mio outside of their house and in the morning shows Mio the footage, explaining its a Shadow that came to kill her. As he is aware of Ushio seeing her shadow, Mio guesses that Ushio told him that and Mio then realizes that Ushio was likely killed by her Shadow.

Etymology

 * The name Mio means "water route, shipping channel" (澪).
 * Mio's surname Kofune means "boat, small craft" (小舟).