Has been a hectic day, so… have some stray crossover worldbuilding thoughts.
The most visible obstacle in crossing Bleach and Darker than Black is the moon. In Bleach it’s there; in DtB, it’s still physically there but no longer visible from Earth’s surface. There’s really no way to compromise on this, so for the Shattered Sky stories (Interrupted Circuit and Distractions so far) I’m just declaring by fanwriter fiat that there’s no visible moon in the shared ‘verse. At least, not in the living world. Hueco Mundo and Soul Society still have theirs.
Other world elements are much easier to fit together. Main characters in both settings are actively avoiding – and in some cases mind-wiping – mundane attention. Put that together with shinigami focusing on the dead, while Contractors focus very much on the living, and the fact they haven’t actively crossed paths in the past ten years is at least plausible.
(Hei doesn’t count. Hei is a weirdness magnet. In fact, from what it turns out his canon power is, he really is a weirdness magnet. Or a creator of weirdness. Take your pick.)
…I’m very sure that Kisuke did a lot of misdirection and no little fervent praying to make sure Aizen kept his attention on the spirit worlds, especially after Heaven’s War took out a large section of South America. The last thing Aizen would need was access to humans with Hollow-like powers.
Then again, Aizen has actual Arrancars to work with. My bunnies say he didn’t even notice Contractors, because they didn’t have enough spiritual power to register as more than a low-level Hollow. Whatever the Gates are, Aizen had nothing to do with them.
This does not necessarily make Urahara feel any better.
One of the DtB canon elements I wanted to explain was the fact that a Contractor who loses their original body also loses their remuneration; the Contract is paid in full, and they can use their power as much as they like. I poked a variety of possibilities, but settled on this: if Contractor powers are Hollow-like powers, then they’re limited by the original human body.
Lose the body, lose the limitations.
Hei, of course, is a special case. But his situation in DtB canon dovetails pretty neatly with what Bleach would define as “mortal possessed by ghost”. Bai lost her body, so she has no remuneration anymore.
Though my take on DtB ep 25, in a crossover context, is that Bai-as-Xing moved on peacefully to the next life once she knew her brother had made his decision. But she’d been living inside Hei’s soul, and one thing we know from Bleach is that an alien power bedding down in your spirit has consequences.
Hei might find things a little more interesting than he’d planned on. 😉