UPDATE, 08/03/07: See Ethan Haas and the Sites of Revelation for answers to most of your questions.
Slusho.jp has allegedly been connected to the Cloverfield Project (a character in the trailer is supposedly was spotted wearing a “Slusho!” shirt).
You can email feedback to Satoshi@slusho.jp, download wallpaper and an AIM icon, and read the history of “Slusho!”
UPDATE I: Received the following auto-reply from Satoshi: “Slusho! loves your mails!! You Can’t Drink Just Six!!!”
UPDATE II: “Noriko Yoshida dedicated her life to refreshment!” according to “Slusho’s!” history page. Noriko Yoshida is a Japanese screenwriter according to IMDB.
UPDATE III: Forgot to mention that the site has a store, a forum (”Happy Talk”), and a section on “Slusho!” flavors that will be available soon.
UPDATE IV: Google searches for Ryouta Yoshida and Ganu Yoshida haven’t turned up much for me, yet.
UPDATE V: “Noriko” means “child of principles” or “child of ceremony; law; order.”
“Ryouta” means “refreshing and thick” in Japanese. Y’know, like an icy-cold “Slusho!”
“Ganu” doesn’t seem to have any pertinent Japanese connections, but “Ganu thora” is the Sinhalese slang name for the “Streaked seerfish.”
Ganu Yoshida had a prophetic dream which resulted in his discovering “Slusho’s!” secret ingredient according to “Slusho’s!” “History” section; one might say he is a “seer.”
UDPDATE VI: “You Can’t Drink Just Six.” Six is the first perfect number. Also according to Wikipedia, “Six is also a unitary perfect number, a harmonic divisor number and a highly composite number.”

[...] Semidi: Slusho.jp has allegedly been connected to the Cloverfield Project (a character in the trailer is [...]
The idea that Ganu found the secret ingredient that “turned him into a whale” and that those who drink Slusho turn into a small whale like Ganu is thematically similar to the story/stories about Dagon which are part of the Lovecraftian mythos — a group of people whose worship of the Elder Gods has mutated them into fishlike creatures similar to the object of their worship.
norika is also a model and a voice actor….
[...] July 11th, 2007 in 1-18-08, Film & TV I was a little absent-minded yesterday when Googling the names at the Slusho! [...]
[...] July 11th, 2007 in 1-18-08, Film & TV Commenter “docangst” notes a possible connection to Slusho! and the use of the god Dagon by H.P. Lovecraft, reviving Cloverfield’s Cthulhu [...]