Oh.
Hang about, didn't Rumiko herself say at some point that she was fine
with people writing fanfiction? (I remember some interview or panel or
something she did that I read.) Does that make any difference to
anything?

Yes, Ratbat-san, it does!

If Rumiko said such a thing, then there is no legal problem with writing
fanfics for any of her works, as that constitutes permission.

If you can actually find a documented reference to such a statement, it
would be a great and wonderful thing. ^_^

BTW, Nice to see that you're still alive, and (reasonably, one hopes) well. ^_^

Ratti

Zen no Itan-sha
Apprentice to the Angels of the Apocalypse