When Hatsune Miku V3 went on sale, two of the 7 previous voicebanks from the Hatsune Miku VOCALOID2 releases were missing "Light" and "Vivid".
Crypton was still discussing with Yamaha conditions which would allow registered users of Hatsune Miku Append to gain access to "Light" and "Vivid" for free.
It was later confirmed that anyone who owned the VOCALOID2 both Hatsune Miku and Miku Append, as well as either of the Hatsune Miku packages (Hatsune Miku V3 English package not included) must register by mid-October to get Light and Vivid for free. The vocals were downloadable until Feb 28th 2014.
These were eventually put up for sale in October 2014, but in this form were sold separately as individual voicebanks.
They were initially made downloadable for free, but required you to register either the Hatsune Miku Append plus the Hatsune Miku V3 package or the Hatsune Miku V3 bundle by mid-October 2013. You would not be able to get this vocal by registering Hatsune Miku V3 English package alone.
Vocal traits as noted:
These are currently the most up to date versions of the two voicebanks as they were never updated for VOCALOID4.
Software issues as noted:
All vocals now are listed as an octave lower than the original VOCALOID2 optimum ranges gave the equivalent vocals as.
They did not come with the "Lite" version of the software and were the only VOCALOID3 vocals like this. You either had to already have VOCALOID3 or Piapro Studio to use these vocals or they are unusable.
The two vocals were the least useful and used of the Hatsune Miku Append vocals. Because of this, plus both their late VOCALOID3 era release and requiring already owning other vocals, many Producers choose to simply skip the purchase of the two vocals entirely and thus far they have been among the least popular of the Hatsune Miku releases.
Cross-Synthesis as noted:
Once imported into VOCALOID4, LIGHT becomes available for XSY. However, LIGHT has no XSY capable voicebanks that can use of XSY as it is a single voicebank release. Therefore users will have to purchase addition voicebanks not belonging to Hatsune Miku at all for use of XSY from her XSY group "Hatsune Miku".
Once imported into VOCALOID4, VIVID becomes available for XSY. However, VIVID has no XSY capable voicebanks that can use of XSY as it is a single voicebank release. Therefore users will have to purchase addition voicebanks not belonging to Hatsune Miku at all for use of XSY from her XSY group "Hatsune Miku".
From Ver.4.3.0 of the Vocaloid engine, a XSY group "Miku V4x" was added to VOCALOID. All vocals within the "Miku V4x" group can XSY with each other. This vocal release is part of this group. If the user owns another vocal from the "Miku V4x" group, XSY between the vocals can occur.
The XSY group "Miku V4x" is the 3rd largest XSY group overall having a total of 12 voicebanks. If old versions that have since been re-released are removed, there are currently 7 unique voicebanks. These voicebanks are; "Original", "Soft", "Solid", "Dark", "Sweet", "Vivi" and "Light".
In total, the combined packages offer the equivalent of 132 additional voicebanks achievable via XSY. The total tone variation offered by the package comes to a theoretical 144 voicebanks in total.
This is not taking into mind the impact of E.V.E.C. on vocal XSY combinations within VOCALOID4 itself.
Note that "GWL" does not become viable for use with any V3 vocals used as the primarily vocal. This should be considered when using any vocal for XSY within the "Miku V4x" group from V3.
XSY is only possible with the full VOCALOID4 software.
Note that unlike many other voicebank updates such as Megpoid V4, the voicebanks have undergone slight changes compared to their past versions. Thus, XSY between "Hatsune Miku V3 Original" and "Hatsune Miku V4x Original" produces a slight change in comparison to "V3 Megpoid - Native" and "Megpoid V4 Native" which has very little change in comparison.