On December 28, 2016, Tone Rion and a new VOCALOID were announced for the VOCALOID4 Engine with a projected release date of February 16, 2017. It was also confirmed that Nemu Yumemi was the voice provider for both VOCALOIDs.
Tone Rion V4 did not receive any demos prior to her release.
Other than access to GWL and XSY, the voice is identical to the VOCALOID3 version and no adjustments have been made to it.
Software issues as noted:
Though treated as different singers, there is sometimes problems with separating Nemu and Rion from each other. When singing something simple that doesn't challenge either vocal, they can often sound very alike and their core very similar sounding. This is simply because they share the same provider for their voices.
When pushed on performance, Yumemi Nemu outshines Tone Rion in a lot of areas leaving Tone Rion as the weaker of the two voicebanks.
Nemu was recorded with the new VOCALOID4 recording style, which allowed more vocal traits to be recorded, while Tone Rion was recorded with the old method style used until VOCALOID3. The new recording style sacrifices ease of use in order to capture more vocal traits. The result is if the pair are compared to vocals of their same type, Nemu in theory will sound more distinct then Rion does.
For Rion, she also is less realistic as she was recorded for her vocal performance over the natural traits of the provider. This is without considering that Nemu uses the new recording method.