If you like nostalgia web.archive.org/web/20071011020350/http://www.pokemon-card.com/products/wcp/campaign/
This is the official website archive where it also says :
« Friday 15 June, pre-order now! Pre-order by Sunday 1 July, delivery on the day of release, Thursday 5 July!
Special sales at the event
Special sales will be held at this summer’s biggest Pokémon card game event, “Battle Road Summer★2007”!
The event will be held at each venue of Pokémon Festa 2007 and Pokémon Pal City, as well as in Sendai and Hiroshima.
The products will not be sold at Pokémon Centers or other general distribution shops.
The number of products sold at the venues is limited. We apologize for any inconvenience caused.
For more information about “Battle Road Summer 2007”, click here. »
I have eventually found the website I once found. It clearly says it was Battle Road Summer 2007 (Festa 2007, Pal City, Sendai and Hiroshima) : park3.wakwak.com/~pokepale/news/0/old/5/z5_011_01.htm
Translation :
« The Pokémon Card Game World Champions Pack, a limited edition product available online and at events, has been announced on the official Pokémon Card Game Trainer’s Website. This “World Champions Pack” will not be distributed to the general public (it will not be sold at Pokémon Centers or toy shops), but will be sold on the official Pokémon Card Game website on July 5. Pre-orders will be accepted on the official Pokémon Card website from 15:00 on June 15, and if you pre-order by July 1, you will receive your product on July 5, the release date. In addition to pre-orders, regular sales are also scheduled to begin at 3pm on July 5th. The packs will also be on sale at the Battle Road Summer 2007 (Pokémon Festa 2007, Pokémon Pal City, Sendai and Hiroshima), a Pokémon Card Game event held in the summer. »
It also says this : « Pre-orders for Pokémon Card Game World Champions Packs, which will go on sale on July 5, started at 3 p.m. today on the official Pokémon Card website, Trainer’s Website. There are two types of packs available for pre-order: 500 yen per pack (up to 11 packs) and 6,000 yen per box (up to 3 boxes). On the card introduction page, three new cards, “Absol ex”, “Sanders☆” and “Fuyou no Stadium”, have been released. By the way, the “World Champions Pack” consists of the same cards as the Pokémon TCG “EX POWER KEEPERS” released only overseas, and some promotional cards used in Japan are included (collection numbers are different from the promotional cards). »
Saying clearly this is purely Ex Power Keepers translated in Japanese as I said earlier.
It would have been extremely strange if this series had been sold the year after its release when we were in full DP series and after the championships for which Japan did not want his players to be at disadvantage (took place in August 2007 in Hawaii), I was pretty sure it was Battle Road Summer 2007