You're looking for Sylvie, Zubis.
As for Shantotto II, wow, I couldn't be more pleased. My targets were the Indomitable Faaz, these are VT. She only uses tier I elemental spells and, as a result, never misses a beat when she has the TP to SC with me or anyone in the party. She'll always hold TP until someone in the party opens a SC.
Nukes for about 1.5-1.8K, WSs were doing 1-2K with 2-3K Light or Dark SC followed by two MB spells, each doing 6-7K each. Even her auto-attacks were doing around 600~ or so. And, because everything she does is considered magic damage, she's deadly accurate.
Two downsides I found were 1) she's a little squishy and 2) she doesn't seem to care what element she uses to nuke . She'll happily nuke away on a target that is absorbing all the damage she's doing.
So, as long as you're using a good tank, like Amchuchu, and not fighting things like Panopts, she's a force to be reckoned with.
She's far and away the best DD trust out of all physical AND magical DD for times when all you care about is brute force. She's a totally game changing Trust. If only all the other DD Trusts performed half as good as her.