Yes, that's me again. I'm answering to my own question (^_^)

I've just tried Hitoshi's seiyuu-related database and it works
like a charm. This is Great work. Congratulations ! 

So, Yokoyama Chisa is the looked for seiyuu.

Well, it wouldn't have hurt Nexus Studios to add a line in the
credits to specify it, in their (old) subtitle.
Or Pioneer could have put a little tsunami picture near Chisa-san photography in the

BGM album #2.
(Maybe the fact she plays tsunami-chan role is stated in the text below. I'm so
brain-disrupted that I didn't checked yet)

Also went to the sasami shrine. But I haven't got Netscape, so no pictures.  (;_;)



	_Greg.