In this fanfic, the plot could center around Naruto being given the claymore sword by a mysterious figure. The sword has a connection to his family that he doesn't know about. Using the sword, Naruto starts to have strange dreams. These dreams lead him to uncover secrets about his past and the future of the ninja world. He must learn to use the sword's power to face a new and dangerous threat that is emerging.
The characters can be integrated by having them meet in a crossover world. For example, Naruto characters could be transported to the Claymore world and vice versa. They could then exchange their fighting techniques. Naruto characters could teach the Claymores about chakra control, while Claymores could show Naruto characters how to use their yoki - enhanced weapons.