Rin-Daughters of Mnemosyne

One of the darkest, most sadistic, and best anime series' around. The story takes place from 1990-2055. The series is about Rin, who looks as though she's in her twenties or early thirties, but is actually immortal. For the first few episodes she runs a detective agency in Shinjuku with her friend Mimi, who is also immortal. While solving mysteries about deaths surrounding them and their friends, Rin and Mimi try to solve the mystery of whose been causing Rin suffering in her eternal life and trying to find a way to kill her once and for all.

The series is comprised of six 45-minute long episodes, each of them taking place in a different year. This is a great series that focuses on relationships, revenge, and the value of life