Suspicious Secrets(2004)

Kizuna

Her younger brother got beat up in the street, and her grandmother died in a hit-and-run accident. One day, disasters suddenly began to strike her family....... Then, a threatening letter arrived, talking about a "secret from 14 years ago"......!　

Can you trust your family? A roller-coaster suspense that opens the door to a hidden "family" secret.

(Source: Kodansha, translated)

Note: The eighth story in the Mondaiteiki (Confidential Confessions) series.