Stained Glass ni Hikari o Tomoshite

The protagonist, Izumi Sumi Ao, wakes up in a hospital. She has lost all memory of who she is and what happened. Moreover, before her eyes floats a glass orb. When she cautiously touches it, she finds herself not in the hospital, but in a church, where two girls are talking. The words spoken by one of them, Yamakaze Midori, sear vividly into her mind: "I'm sorry." Why did she say that? What has she forgotten? Guided by the memories within the glass orb, she begins to reclaim her own past.