篠原 世以子

Likes: Doing her hair, interpretive song and dance
Dislikes: Being alone
Hobbies: Text messaging, keeping an observation diary on Naomi

A student in Kisaragi High class 2-9. Lives very close to Naomi, and generally accompanies her to and from school each day.
A free spirited, she often says or does things that take others by surprise -- though she's also easily forgiven due to her good nature and amiability.
Her mother disappeared three years ago, leaving her with three younger siblings and a working father. As such, she basically serves as head of the household.
Seiko seems to regard Naomi as a kindred spirit, and the two of them frequently have long conversations about their many dreams for the future.

In the events of Corpse Party: Blood Drive, she is discovered by Ayumi, trying to communicate with her through an ouija board and cannot be seen due to her low spiritual qualities. She tells Ayumi to tell Naomi that she is alright even though it is quite oblivious she is not, but doesn't want Naomi to worry about her, and still deeply cares about her even in death.