are y'all ready for a pjo headcanon that works but is also way too far-fetched
It's about Bianca di Angelo. Just keep reading, it'll make sense.
When we first learn that she chose to be reborn, it's in Son of Neptune. It's from Hazel's pov, but Nico is telling the story:
"I saw her spirit a few times in the Underworld, except that the last time I went down there...”
To bring her back, Hazel thought, though Nico didn’t say that.
“She was gone.” Nico’s voice turned hoarse. “She used to be in Elysium—like, the Underworld paradise—but she chose to be reborn into a new life. Now I’ll never see her again." - Nico di Angelo, in The Son of Neptune.
That is the only moment when Bianca's rebirth is mentioned (I've scanned the books for other mentions of this but I haven't found any, so please tell me if I'm wrong on this one).
That's pretty solid proof, until you think of multiple things:
- The first second Bianca had the chance to get a life of her own and no longer need to care 24/7 for her brother, she took the opportunity.
- In Battle of the Labyrinth, she wasn't very pleased every time Nico summoned her, and kept telling him he had to let her go. She didn't even show up unless Percy was there:
“Let’s ask Bianca.” The sky seemed to grow darker all of a sudden.
“I’ve tried,” Nico said miserably. “She won’t answer.”
She turned toward her brother. Her expression was sad, as if she’d been dreading this moment. “Hello, Nico. You’ve gotten so tall.” “Why didn’t you answer me sooner?” he cried. “I’ve been trying for months!” “I was hoping you would give up.” - Bianca di Angelo, Battle of the Labyrinth.
I think it's safe to say she doesn't want Nico to contact her. She wants him to move on from her death and live a happy life of his own, without constant grief. So, if Nico was unable to find her, she probably chose to be reborn.
Until you go in the Cabin 13 wiki and find this:
"Umbrakinesis: They have control over darkness and shadows for various uses such as solidifying it for attacks or to hide in it. [...] Invisibility: They can use shadows to cover themselves in darkness to become invisible."
Neither Nico nor Hazel have similar shadow-related powers. Nico's are over the dead, and Hazel's relate more to precious materials. Both of their powers are in no way similar, and we can also see that among siblings, powers tend to vary (take the Apollo cabin, with Will (healing), Kayla (archery) and Austin (music) for example).
What I'm trying to say is that there's a possibility that when Nico went to the Underworld for the 100th time looking for his sister when the Doors of Death were open, and Bianca wanted him to get over her death and stop contacting him, and also had possible invisibility powers... There's a chance that she just hid from him, told Hades that she didn't want Nico to be able to find her and to tell him she chose rebirth if Nico asked, and force him to move on.
We haven't seen a lot of her character since she wasn't present in a lot of the books, but I feel like this is definitely something she would do if it meant that her brother would be better off in the long run.
Conclusion (/TLDR) : she might have faked her rebirth to make Nico get over her death once and for all.