The secret escaped experiment

Almost four years ago, a three-year-old girl disappeared on her birthday.
Her case was filed. Archived. Forgotten.
Until the day Inspector Akane Tsunemori and Mika Shimotsuki find a small, unconscious child lying in the middle of the street.
No ID. Weak breathing. Bandages stained with blood.

A quick search confirms it - the girl matches a three-year-old missing persons report.
But this is no ordinary reunion.
Because the child is not just a victim of abduction.

She is the little sister of Kirito Kamui - the man who once stood against the Sibyl System.
What happened to her after she vanished?
Who kept her hidden all these years?
And why does her existence threaten to reopen wounds the system tried to erase?

Some cases are closed.
Some experiments are not.