Perhaps I should have clarified my first question, a bit:
 I _am_ familiar with the _characters_ of Yuka, Sayuri, Hiroshi, and
Daisuke;  I was more curious about the origin of the names - whether
they (the characters) were referred to by name in the manga or anime, or
rather had come to be associated with these names from time long
forgotten, by virtue of some primordial fanfic.

Hiroshi and Daisuke and referred to by name in the 3rd-season story
"Ghost Story!  Ranma and the Magic Sword" (on the "Suddenly Sasuke" tape).
There's a brief scene where Ranma comes on the two, lying in an
unconscious heap, and says something like "It got Hiroshi and Daisuke
too."

Not sure about Sayuri and Yuka, sorry.

Angus

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Angus MacSpon                                                Allen Gainsford
http://shell.ihug.co.nz/~macspon/          http://shell.ihug.co.nz/~macspon/