The Takara Bank Case is an unsolved case from around 1978 or 1979.
In the late seventies, the Yamashita Branch of Takara Bank closed when the branch and assistant manager both died of heart attacks on the same day at roughly the same time.
Soon after, other members of the same branch began dying sudden deaths (the cause of which is never specifically addressed), and the final death was a suicide. It was later discovered that others associated with the suicide victim also died under "strange circumstances".
N-Suke Yamanaka, who had worked on the case, theorizes that the events of the Takara Bank Case have some sort of connection to a string of recent deaths of students by heart attacks. He then comes to the conclusion that, if this is true, more students in the school will likely die as well.