When I was righting a fanfiction I can to a realisation that Nico might know the conclusion to the Prophecy of Seven. Think about it. He always spends time in the Underworld with his dad, so secrets can come to him easliy and who knows where else he's traveled. Plus he was the one that brought Hazel back from the Underworld conveniently around the time the pophecy started happening. He must have been going to the Camp Jupiter longer than Hazel, but how did he know about it in the first place? And when he first got there, how did he know he shouldn't say anything about being Greek? Why didn't he say anything about knowing Percy, and why try ignoring him. Also, Death said that only a special demigod can find the Doors of Death, I think it was Nico and thats why he went, the only bad thing was that he unfortunately got captured. I think he went looking so that, when the time comes, he can show the seven where they were. Also he said Bianca was reborn, could she also play a role?