[orion]

Originally Posted by Shinji103

I know they were originally planning to kill Yin, but they didn't. After that, there was no point in keeping her locked away if she was dead or they wanted her dead. Whether we see tubes or not, it doesn't change the fact that there wasn't any point in keeping her in that box at all if she was dead or they wanted her dead. And if it was just going to be a slow death, then there was even less point in locking her up. All they'd have to do is shoot her. Why spend the time and money with the box and the guard? Just kill her and be done with it. But they didn't. Which proves they later decided to keep her alive. As "Golgo 13" said, when Suou's attack back in episode 6 woke her up, they had hoped she would choose to seal herself away again, which means she was still alive in that box and has been since, until she left her body. And she only "died" when she left her body.
As I said, for all we know the box may have been a stasis chamber, for which there would be no need for tubes. And just because we didn't see any tubes in the box the one time we saw inside it doesn't mean it wasn't meant to sustain her life. They're using hover cars and flying cars in public; who knows what kind of medical technology they have. And as I said some time before, what's the point of the oxygen mask if they're just letting her die? She'd have died long ago if she wasn't getting sustenance, at which point the oxygen mask is completely pointless.
None of this makes any sense; if they're just going to let her die anyway, then there's no point in the box, sealing her up, or the oxygen mask that we do see. It's obvious the box was meant to keep her sealed up, but alive. As you said, they should have just killed her from the start, if they weren't trying to keep her alive. The fact that they didn't disproves the idea that they were letting her die.

And about the strangling with tubes part, I think you're reaching way far there. Where's the evidence that she'd use physical violence? Nobody has even said that she was actually murderous. The only thing we've seen is that she's killed a bunch of Contractors. Hei has done plenty of that, too. We didn't and don't know Yin's reasonings for what she did yet. For all we know she may have thought she was helping people by killing bad guy Contractors (all the Contractors we've seen her kill have been bad guys, after all), and wouldn't attack anybody else. Either way, there's no real indication that she'd turn into Jack the Ripper, break open her box, and violently kill people with tubes.

The fact that she wasn't killed outright doesn't prove that they were trying to keep her alive. They did what people do for certain endstage of life people nowadays. No IVs. No nutition. Just keep them comfortable with oxygen and let them go on their own. Plus, if they had killed Shion, she would have been turned into a weapon or an energy source. So the oxygen had a duel benefit of keeping her alive if they got to Shion and keeping her comfortable to allow them to let her go if they didn't. And with not much support staff, her continued existence wasn't a high priority imo.

And there's no indication that she wouldn't kill her captors either. They're law enforcement with a prisoner who is a known killer. You don't go making assumptions that the prisoner won't turn on you especially when she's 1/2 of the Apocalypse imo. Lucy was very adaptable with what little she had to escape in Elfen Lied. It's not unreasonable to assume Yin couldn't otherwise also.