Hatsune Miku: Future Delivery

In the distant future, Asumi--a girl who has no clue to her memories but a drawing of a green-haired, ponytailed person--finds her only friend in Asimov, a battered old delivery robot. The strange companions travel the stars together in search of the mysterious ''Miku,'' only to learn the legendary idol has taken different forms on many different worlds!

(Source: Dark Horse)