Well, a really cool plot could be that the Tailed Beasts in Naruto are somehow related to the Gates in Darker than Black. Maybe the power of the Tailed Beasts can be used to open or close the Gates, which has a huge impact on both universes. And the characters from both Naruto and Darker than Black have to work together to stop a greater evil that wants to use this connection for its own malicious purposes. This would involve a lot of action, mystery and character development as they learn to trust each other.
One plot idea could be that Naruto characters gain the powers of Contractors from Darker than Black. For example, Naruto himself could have a Contractor power related to his shadow clones, like being able to send his clones to different dimensions for a short time. Another idea is a story where the organizations in both universes collide. The Akatsuki from Naruto and the Syndicate from Darker than Black might have different goals but similar methods of achieving them. They could either fight or try to make an alliance depending on the situation.
A possible plot could involve Sasuke as a Contractor. His power could be something related to his Sharingan, like being able to see the true form of Contractors and Dolls. This would put him in a unique position in the crossover. Also, the story could focus on how the characters from Naruto adapt to the much darker and morally ambiguous world of Darker than Black. It could be a journey of self - discovery for them as they face new challenges and enemies that are not as straightforward as the ones in their own universe.
Chapter 258, "Troops at the City Gates", is the clearest early answer because it pushes Nes Luman into a new phase or setting. It opens with Gu Hang and Wang Qi, this mother and son duo, discussed post-war... and closes on Through his military binoculars and the reports from his....
Chapter 233, ", Roll In", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. It opens with The Chaos Octagram Array that connected to the real world was guarded... and closes on If the goal was just that, the people already present would have been....
Chapter 248, ", The Death of Titan", is the clearest early answer because the violence around Knight Titan becomes final instead of hypothetical. It opens with He did notice, but while communicating with his comrade, he got... and closes on A Plasma Charged Gun shot hit right at his already faulty left knee.. The key payoff is that the chapter closes with 4.3k!, which gives Knight Titan a stronger narrative position and pushes the power growth onward.
Chapter 273, ", Sun Lord (6k additional)", is the clearest early answer because it turns Solar Expedition's situation into a concrete plot event. The setup is Some positions appear regularly, contingent on the current political..., but the pressure keeps building through This type includes a great many, such as the representative of the....
Chapter 176, ", Making Dumplings", is the clearest early answer because it turns Making Dumplings's situation into a concrete plot event. The setup is He stared blankly at the pitch-black muzzle as it emitted a burst of..., but the pressure keeps building through Following the charge of the troops, Colonel Perbov, who was several....
Chapter 224, ", As the Thought of Alliance Emerges", is the clearest early answer because a shaky connection becomes usable in the plot. The setup is Facing Georgette's frustration and dissatisfaction, Gu Hang felt..., but the pressure keeps building through Superior Georgette, I am very regretful as well..
Chapter 248, ", The Death of Titan", is the clearest early answer because the violence around Alliance Army becomes final instead of hypothetical. A useful checkpoint is the way the scene starts with Heijian Star, Capital Pansel City of the Luman Kingdom, and the... and follows through with They might not penetrate the armor, but under the assault of several....
Chapter 293, "You want 300 million?", is the clearest early answer because it turns Gu Commercial Firm's situation into a concrete plot event. Early on, Furthermore, deciding whether to turn a blind eye depended on.... By the end, People would rebel against them in an instant.. Inside the broader family politics storyline, the chapter closes with Then, the inspection began., which gives Gu Commercial Firm a stronger narrative position and pushes the power growth onward.
Chapter 273, ", Sun Lord (6k additional)", is the clearest early answer because it turns Smart Mechanisms's situation into a concrete plot event. The chapter turns that into something concrete by moving from Through the glass window, Gu Hang watched the restless little boy... to It was a deeply reluctant decision born out of necessity..
Chapter 237, ", Can I Also Ascend to Godhood?", is the clearest early answer because it turns Gu's situation into a concrete plot event. It opens with They might not understand much, but seeing Mr. and closes on Her softened attitude, the assistance she spoke of, paradoxically.... The key payoff is that the chapter closes with Or... to ascend to 'godhood' by means of the body of the slain Evil God?, which gives battle a stronger narrative position and pushes the power growth onward.