Radioactive elements and hydrogen cyanide are placed in this box.

Inside is also a Geiger counter, and when alpha particles emitted by the radioactive elements are detected by it, the hydrogen cyanide will be released.

Youmu-chan is put inside.

One hour later

Now is Youmu alive? Or is she dead?

we can't know without opening the box.

Well,

The answer is half-dead! Literally, "half-ghost".

Right, whatever, just let her out.