if i wait for the shiver (just need recipe) then i will have steller set but i would like a sword to help with vana (i grind the tokens for the acient plate sets and sell them ^-^) so it isnt a pain in the butt on the mask stages of vana
should i make civ with UV undead low or wait for shiver
You already grind Vanaduke, converting 30 Almirian Seals into 30,000 crowns every 10 trips or so? Then you don't need our help, right?
Or are you planning to grind Vanaduke? What are your current weapons? Are you saying that you have the 4-star versions of both of these, and want to know which to upgrade first? Then I'd recommend the Shivermist Buster, because then you can freeze Vanaduke in phase 5, and this makes you much more useful to parties. (I don't think that the 4-star version has a big enough radius.)
4* has a big enough radius, but real risky. I saw someone poison vana with the 4* venom veiler, but it included a lot of running. Should also be noted that the poison status only required vana to be within range less often than freeze is required. Thus, this adds more risk.
The achievement itself is not a huge part of the game. It gives no bonuses, and you are better off thinking in terms of usefulness in upgrading, than simply filling each achievement.
If you don't have a 5* weapon yet, do the CIV. You'll need as much power in your main weapon to help out your teammates the most.
Shiver will help you and teammates out more by shiver locking Vana in place. Vana's mask phases are easy enough that it really doesn't really matter what sword you use. Undead low on a CIV is a subpar UV for it anyway. If anything you'd want at least a CTR medium.
Heck, CIV isn't even the best choice for FSC IMO, but that's another argument.