This is really essential watching for Dead Aggressor. There is lore and character development here thats very important. When to watch? You can watch first, or you could watch after episode 4 (allowing Dead Aggressor to introduce the main core concepts first). It presumes you've watched Dead Aggressor so I can't say its spoiler free, but the context outweights these minor parts in my view. On its own? Its a decent story on its own part, with solid action and likeable characters with a clear and complete arc as well as tying well to the wider Fafner story. I will say its tries too hard toplay the tragic hand when its got such a short time to introduce its characters, and a couple of elements felt forced near the end- but its overall a success.