"Hikaru ga Chikyuu ni Ita Koro" series by Nomura Mizuki. The mystery regarding Hikaru's death from volume 1 was resolved in volume 10, although that's relatively a non-event. The real highlight was how every character existed to fulfill a particular role, and all these roles together formed a well-rounded drama. The careful attention to explain the purpose of each character's existence in the final chapters was very well done.
Other than Hikaru being quite an annoying character throughout pretty much the entire series, overall it was very good series, with well rounded characters and a very complete ending. It's a love story that is well worth reading.
Previous (2014-05-09): "Hikaru ga Chikyuu ni Ita Koro" volume 9 by Nomura Mizuki
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