A Complementary Voice in regards to Vocaloid, are a duo of voices made to match each other.
Usually by design they have a particularly style, but will often be designed to achieve that same style in a different way. For example, one may have lighter tones and the other deeper, Or one might have more solid sounds and the other looser. This is why in most cases the vocals are sampled from a male and a female vocalist. They are also referred to as "counter partners" or "counterparts" for this reason.
The duo will by default tend to sound well together naturally because of their design intentions. In addition, they will often sound better together naturally then most other vocaloids for the same purposes when paired up with either counterpart.
- Leon/Lola; both are soul singers. Leon is a light and airy masculine vocal while Lola is a deeper toned female with a reggae vibe.
- Meiko/Kaito; originally they were designed to be a pair of male and female professional vocalists.
- Kagamine Rin/Len; a pair of vocals sampled from the same vocalist, they represent both "male" and "female" and are designed for both harmonizing and contrasting with each other.
- Prima/Tonio; both opera/classical style singers, Prima being a soprano singer and Tonio being a baritone/tenor.
- Sweet Ann/Big Al; both cover classic rock. Sweet Ann focuses on a "sweet" sounding mature female while Al focuses on a deeper mature male vocal and a rougher timbre.
- Bruno/Clara; the first two spanish vocals followed the traditional male/female complimentary voice set.
- VY1/VY2; the standard male and female Yamaha voices for Japanese.
- Dex//Daina; a pair of English American accented Vocaloids with a "fox and hound" theme. Dex is a "power" type male vocal and Daina is focused on a softer female tone. Both are pop singers.
- CYBER DIVA/CYBER SONGMAN; the standard male and female Yamaha voices for English.
- Merli/Aoki Lapis; opposing rival voicebanks intended to represent "light" and "dark" traits.
The following is a list of intended vocalists who are designed to be a duo, but their counterparts have not been released.
- Avanna; was intended to have a male counterpart. The male vocal was never released because Zero-G could not find a suitable voice provider for the role.