Killing 1 white nevron

[★ X]

If i killed 1 white nevron and helped the rest do i need to repeat every white nevron quest on NG+ for achievement or do i have to only do the one i killed?

[Aveax]

did you talk with the last white nevron? (the one with hands) if not then go there and if you are unable to talk or something then NG+

[Sharkinbear]

If you spare all of the white nevron after doing their quests, the nevron, Blanche, located at the fountains gifts you 100 colours of Lumina. If you kill even one of them, you will have to fight blanche. He only gives you I think like 30 colours of lumina instead. Either way, completing all of the quests no matter how you finish them will give you credit for the achievement.