Hatsune Miku
Hatsune Miku was the first Vocaloid developed by Crypton Future Media after they handled the release of the Yamaha vocal Meiko and Kaito. The name of "Hatsune Miku" was conceived soon after the Vocaloid 2 announcements, when an English and Japanese vocal were developed for the character. The intended design was delayed and later used for Megurine Luka instead. Miku was intended to be the first of a series of Vocaloids called the ""Character Vocal Series"", which included Kagamine Rin/Len and Megurine Luka. Each had a particular concept and vocal direction.
Hiyama Kiyoteru
Silhouettes for the AH-Software Vocaloid 2 vocals were revealed on a poster on November 6, 2014; however, it was unconfirmed what they were for at the time. On November 20, it was confirmed in the livestream for Vocaloid 4 that they all, with the exception of Tohoku Zunko, would receive updated vocals for the new engine. Kiyoteru's new vocals were recorded from scratch to improve his upper and lower ranges. Kiyoteru was confirmed to receive a "Natural" and "Rock" vocal for his Vocaloid release, allowing him to make use of the cross-synthesis feature in Vocaloid 4.