In GOOD NIGHT WORLD, Aya is the sister Taichiro and Asuma lost when they were very young. Inori Minase voices Aya.
The loss of Aya resulted in the growth of Taichiro’s hatred towards his father. Aya was Asuma’s twin. However, she was nothing like Asuma.
Aya was slow to learn things at home and school. All she ever did was smile and apologize for being that way. Hence, nothing she did ever made their father, Kojiro, happy. Kojiro strictly wanted a perfect family, not for his family’s benefit but for his own.
Aya’s death
One day, Aya forgot one of her notebooks at school. It was nighttime and past 10 o’clock, and even then, Kojiro made Aya walk alone to the school and bring that notebook back.
It kept getting late, and Aya didn’t come back home. The family later learned that Aya got into a traffic accident.
At Aya’s funeral, Kojiro refrained from taking responsibility for his daughter’s death by claiming that, just like every other traffic accident, it was unpredictable.
Taichiro has stopped seeing Kojiro as his father since then and has grown to hate him more than any other person in this world.
Kojiro’s secret
In the finale of GOOD NIGHT WORLD, Kojiro confesses that Aya’s death motivated him to create powerful AIs, which became his ultimate dream, and the Black Bird came into existence.
Kojiro says he wasn’t in his right mind when he created the Black Bird, as he didn’t consider the risks that would come with it. Kojiro never told anyone about his motivation, not even his assistant, Kamuro.
Kojiro did name the Black Bird Aya, but only in his head, hoping that the name would become its identity. In their last moments, the Black Bird, as in Sasumata, appears as Aya and dies alongside Kojiro.
