Memory Diary is a diary that Toro used in TORO! Let's Party!. The Memory Diary, so it is told, can grant any wish when all of it's pages are filled with "thank-yous".
Thank-yous can be received by making people happy, or by helping them, so they say "thank you". The Memory Diary gives a visible glow when a thank-you is cataloged.
The Memory Diary was originally in the possession of the Crescent-Scar Cat, and perhaps was created by them as well. While it is unknown if the Memory Diary truly has the power to grant wishes, after Toro seemingly used the diary's wish, the diary could no longer be seen glowing upon hearing a thank you.