Birth
Decades ago, when Airi was a young girl, her best friend Hana once stayed at her house for a while, shortly after Hana's mother passed away.
Airi's family was well-off, and as an only child, she was doted upon and grew up without experiencing much hardship, appearing somewhat naive and silly. Hana, on the other hand, was different in both personality and background. They had known each other since they were very young, becoming friends so naturally that Airi couldn't even recall what brought them together. Year after year, their bond grew stronger and closer.
That year, Hana's mother died when in pregnancy, leaving behind a grieving family. Hana had a falling out with her father and refused to go home. After staying with her grandmother for a few days and being driven out by her aunt, she had nowhere else to go and ended up at Airi's place.