I shouldn't reply to an old post, but I will leave this here for people who may end up here like me.
In the Nasuverse, or at least in the Fate series, the usage of "traditional D&D alignement" isn't precise. Well, it is precise but in a different interpretation.
The Good vs Evil axis regards not the moral of the person but his personality. Good and Evil are personality types, good means open, brave, honest and magnimonious. Evil means selfish, cowardly, sly and focused on self-gratification. It also regards how, even unconsciously, a person see himself.
For example: Medea knows that what she is doing is bad/evil (harming people for her own good), and she does so following a selfish desire.
Meanwhile, Gilgamesh, who want to fuck up the entire world is doing this on a honest proposal to save humanity. In his own way, but that's his objective.
Law and Chaos are principals- Law means you care about some likely very abstract concept to the point of total self-denial. Chaos means you feel no obligation towards anything but your own whims.
A Lawful-Nasu character, also, follows more rigid and generally good (in our traditional interpretation) morals, while Chaotics are generally connected to no-morals whatsoever, only thinking about their true desire, and so are more "evil" in a traditional way.
This is shown, again, in Gilgamesh and Medea, with a little bit of Cu and Saber.
Gilgamesh (chaotic) even if he is working to improve humanity, he does so without any consideration for little lives but an eye on the general condition of the race. Killing something like 90% of humanity is good, if it helps the remaining 10% to reach a better condition.
Medea is evil indeed, but not without any consideration. Just watch how she harms people, but avoid kills and has a particular hate for harming children.
She isn't complitely without any moral lines.
While Lawful sees a perfect example in Saber and I guess that it is enough. Moral, putting oneself in danger for a greater good, following a (strict) code of behaviour and so one. But she is Good. Cu is an example of the same thing, but on a neutral level.