Love Letter

Takuya works as an assistant professor in a medical school, and with his talent, he shows promise not only in the academy, but also in the medical society.
One day, Takuya receives a letter from an unknown sender. Though he thinks it's suspicious, he still opens it and finds a piece of human skin inside.
Then afterwards, the bewildered Takuya continues to receive letters written by "The woman who loves you the most in the world". The contents of the letters gradually continue to escalate, and finally it reaches a point where video recordings of women close to Takuya being brutally murdered are sent to him.

[from Getchu]