As unpopular as DDD itself. A story featuring featuring “Ookumaneko Mokumoku” -until then just a side character- and a well-known little sister: “Ishizue Kanata”. Shunji Enomoto drew a short manga based on its events (pic related).

Across the story we can see a Kanata with the urge to kill some time (and other things), making her way out of her chamber (more like a prison) with the help of the docile Origa Vice-president. Then, Kanata resolves going to a room nobody has stepped in for a long time. That room was located in her own ward; “Ward D” and its number was: “The Room No.404″, however, as this room was a mystery to even those patients (monsters) of Ward D and even though what lied inside resulted very attractive to pry into, no one tried doing it before, after all, the Hospital files didn’t even consider an active room anymore.

Before she destroys the iron door intruding in her way, a dim, puzzling voice spoke a few words, resembling a warning to her:

“Don’t come in. Don’t come in. You cannot withstand my power. If you come in you’ll regret it.”
“Cherish life, don’t enter my world.”

…this of course was the voice of Mokumoku, a 30 years old NEET who hid an unimaginable power.