It may be Vocaloid 2 Hatsune Miku.
It was MEIKO. Out of all 5 VOCALOIDs KAITO was considerd as a failure. After Hatsune Miku was released, and KAITO appering in her videos, MEIKO dissaperd from Crypton top 10, and KAITO became one of the top 10.
Hatsune Miku had 20,000 pre-orders and more than 40,000 sales. Megpoid was able to reach the popularity of Hatsune Miku, getting updates, english, and native.
The ones considerd as most famous is IA-ARIA ON THE PLANETS and MAYU. But the only VOCALOIDs who we only know were able to be sold well is YOHIOloid selling more than 10,000 copies and downloads, and KAITOV3, beating Hatsune Miku on the top 10.