A good name for my manga?

It sounds like a pretty cool read! Unfortunately, without knowing the events of the sequel it might be hard to think of something. You should add detail about the sequel's plot that is different from the first, like some issue that still needs to be resolved; and you should have some examples of what you do/don't want, like if it's going to be a series, do you want "Grim:" in the name too? Sorry I couldn't give a suggestion though.