Case 70 is the PRT designation for a pair of capes who share a single body and have similar powers. So-called due to the phenomena being the 70th anomalous case in total the PRT investigated. A Case 70 situations occur when twins trigger while in physical contact with each other.
In Capricorn's case, only one of the twins was in control of their body at any given time. The inactive twin shared the perceptions of the active twin, but had no way to interact with their surroundings. Only the active twin could pass control to the other, causing their body to transform into the other twin's body. Clothes, armor, etc, is also switched over.
The twins Nix & Nyx are not an example; they may have been an attempt to replicate the phenomena.
Extremely pedantic people will point out the twins do not have completely identical DNA. Obviously what DNA the shards do use to lock onto their targets is not noticeably differentiated between hosts.
↑ 1.01.11.21.188.8.131.52.71.81.9“Case seventies in North America included Knot, Tandem, Zigzag was one, I think, there was House of Three in Quebec. And… you, it seems.”
“One or two of them might not be seventies, but they get called seventies because they’re close enough. Blurred lines, like you said. When twins trigger, the powers are identical or nearly identical. When twins trigger and they’re touching one another, like you said to Rain, things get blurry, the agent is too stupid or careless to tell where one starts and the other ends, or it wants to fuck with us, and it jams everything in together. Two minds, two similar powers, and one body to be shared.”
“Is he asleep?” I asked.
“No. He’s in here, he’s watching and listening. He sleeps when I sleep, or I sleep when he sleeps, if he’s in the driver’s seat. We trade out for two hour shifts.”
“Can he communicate?” I asked. “Talk to you while it’s your turn?”
“That would be too easy,” Tristan said. His good humor was gone now. He just looked sad. “No.” - Excerpt from Flare 2.6
↑Official files. Classification documents. Then there were the notes for case one, case fifteen, case thirty-two, case fifty-three, case ninety. The ‘cases’ were the events the PRT had deemed of interest. Riddles both solved and unsolved. My collection there was incomplete, but some were official enough to be confidential, and I’d never had that access. Others were closed, the mystery deemed nonexistent or something to be folded into popular knowledge. - Excerpt from Daybreak 1.1
↑“Tristan couldn’t switch to me, I don’t think,” Byron said. “When we were talking about capes we might run into last night, we theorized it was a thing we could do, that if he switched to me I might not be compelled, but he didn’t switch.” - Excerpt from Shadow 5.10
↑The Heartbroken had made it to the gates and were crossing the floor. I could tell by the color schemes. The retreating wounded were at the exit we’d come through and cleared. Tandem was now two people, running hand-in-hand. Another Case Seventy, like Capricorn. - Excerpt from Dying 15.3
↑Prisoners 604 and 603, Knot, were happily gorging themselves on food in Cell Block Y. Despite their cognitive impairment, they had fallen into a role as enforcer and heavy hitter for Prisoner 390, leader of their cell block. Prisoner 390 had had a son – she could only hope that he would find some similar affection for Knot, with their childlike mentality. - Excerpt from Interlude 10.5
↑cite comment about zigzag not getting an explanation until the sequel
↑Lunatic Blue: I have a question, what does the Butcher mean for shards/entities? Is it an aberration?
Wildbow: keep in mind that the shards are pieces of the entities, they have residual effects & processes from being part of a larger organism, so where stuff isn't skewed intentionally, sometimes you just get quirks running through. - Wildbow on Discord, archived on Spacebattles
↑“Dealing. Some days I’m fine, some days it catches up with me and I’m the furthest thing from ‘fine’. It’s times like that where I think a lot about-” He lowered his voice. “-how there’s not a lot of case seventies left. Even before Gold Morning, most were dead or they had totally gone off the deep end.” - Excerpt from Torch 7.6
↑sanctaphrax: What was the deal with Nix and Nyx, anyway?
Wildbow: Twin sisters, took Cauldron vials, one went Case 53. - Comment byWildbow on Reddit
↑Fenja and Menja share powers for the same reason the clones draw on the same shard. The shards use DNA as an identifier for who to tap into/reach out to. If one twin has a Corona Pollentia and the other doesn't, then only one gets powers - Unusual powers