Japanese seiyū: Yumi Kakazu
English voice actor: Cynthia Martinez
First appearance: Episode 1
Hiroko Asahina is a classmate and friend of Ayato and Mamoru Torugai. During the attack on Tokyo in episode 1, she is lightly injured, and bleeds red blood. While Ayato is in the real world, her Mu phase activates. When Ayato returns to Tokyo Jupiter, Hiroko is relieved to see him again but is distressed by the memory loss resulting from her Mu phase activating and a feeling that Mamoru's explanation for Ayato's absence is not right. Later, she is shot by agents guarding Mamoru; Ayato finds her, and she asks Ayato "It's red, right?" while she is covered in blood (now blue) from her wounds. Ayato assures her that her blood is red, but they are afraid to admit to each other its real colour. When Ayato leaves Tokyo Jupiter for the second time, she leaves with him, and the two of them live together for a short time. While she is with Ayato, she has terrifying visions of herself as a Mulian bound to a Dolem, but cannot bring herself to talk about this with Ayato. However, she keeps a diary where she can write down her feelings. Her Dolem Vibrato eventually shows up, and Ayato destroys it, killing Hiroko in the process, which deeply traumatizes Ayato. At the end of the series, when Ayato re-tunes the world, Hiroko (as well as Mamoru) is brought back to life.
It is revealed, through flashbacks in the series as well as in the movie prologue, that Hiroko was in love with Ayato while they were in their early teens, before Tokyo Jupiter was created, and that her feelings have not subsided even though she is dating Mamoru.
Asahina's role in the movie is identical to that in the TV series.