LOVELESS ～終わらない物語～

Around the year 200 AD a girl was born as the first 'qualified person' in human history. She went on a journey to find the species as herself. She met three friends during the following 1800 years trip. And together they went on journey again to find the 5th person. He turned out to be the first man from the 'qualified person' species and the protagonist of this story. The existence of five qualified persons at one place and time attracted a monster called "a heteromorphic person", and their fateful encounter is drawing near.

[From vndbreview]