Rikka is Kuro Sakuragawa's older cousin and the reason he visited the hospital as regularly as he did. Just like Kuro, she also has the powers of immortality and precognition, although she wants them to be removed and has tried medical science and suicide to no avail.

Spoiler

Due to this, she later switches her plan on creating imaginary monsters such as Steel Lady Nanase with god-like powers, hoping that they would eventually be able to turn her back to normal.