Manga Like Haruiro Astronaut

Mami and Chiki have always shared everything in life. They are identical twins, yet so different in character and personality: Mami tender and helpless, courted by boys to whom she never says "no" to, Chiki with a strong sense of duty and a great spirit of sacrifice, would do anything to see her sister happy. But then comes a time, however, when one realizes there are things that cannot be shared, especially when it is something extremely rare and unique .... just like an alien?! Haruiro Astronaut is published as extra chapters in the series "Orange" by the same author.