I'm working with a friend on a story about native americans/first nations on the technological level of 16th spaniards conquering germanic tribes in the european 4th century AD. The story has a dark, realistic, gritty, sometimes even gory atmosphere.
I'm the one responsible for the story, but I have to work in reverse order than usal. Usually I have characters in mind and know the societies I will place them into and from there on I develop the story, but here the story comes first and I have to adjust characters to the story. For me that's pretty tough and I lack ideas for germanic characters.
I know, ideas are precious and you're not likely sharing your ideas with me, but perhaps still...
I can add plot details too.

I don't really understand what you're asking for. If you want 'germanic' characteristics, you'll get that through researching what germanic people of that age were like, what they valued, etc based on social anthropology. If you want character traits and development, you do that on a personal level based on the needs of the story. Traits like loyalty, intelligence, etc have nothing to do with the region a person is from.

Or am I missing the point?

So are you asking what was germany like in the 4th century?