Song Magic that requires more than one singer is quite rare. However, Reyvateils can sing together and combine their power under the proper circumstances.

For example--Luca and I are used to singing side-by-side in battle. Although I could not sing Luca's Song Magic by myself, I can sing to support her magic. Song Magic sung as a duet is stronger and evolves much faster than when it is sung by a single Reyvateil.