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Shogakukan has posted "My Sweet Sunday," the one-shot manga short story that acclaimed creators Rumiko Takahashi and Mitsuru Adachi created this month to celebrate Weekly Shonen Sunday magazine's 50th anniversary, on its Club Sunday website. (In the linked page, select the yellow button labeled "読む" on the lefthand side.) The story will be remain free for reading in Japanese from March 25 to May 24.
Sounds fun I just checked out the site and it seems it is really the same manga. Each mangaka drew each couple of pages in turn.
Can't wait for the translation