They both come from a world where mercy to monsters and misshapen experiments inevitably painfully backfires. Letting any of these cyborgs go would .. do what? Put someone else at risk later? Let the rest of the swarm know where to find them? No one from Gaia would judge Tifa for deciding to kill the trapped cyborg, and as she hesitates, distracted not by morality but by his own speaking up, Sephiroth heads for it himself to see to its demise - after all, she has smaller, more toothy things to worry about.

He's watching though. Her fighting style didn't suggest ninja to him, and he wanted to observe further; interference if necessary, but if it wasn't? "Even so, as mine are." Inert, pretty glass beads and not much else. They could be removed from Masamune or put back in, but ... nothing else remained of their power. Still, if one was functional, maybe the rest in time.. "I had thought something nullified them all, but it seems not. Is it mastered?" If not, it could seed other ones. With time and effort, one blizzard would wind up many more.

Tifa's snarl doesn't sound like a noise a human throat makes, and even as the cyborg is efficiently decapitated with Masamune, he's watching closely. If it becomes necessary, he can interfere, but it's just one cyborg hound, isn't it? And ...her teeth aren't quite right anymore either, are they? Almost absently, he runs his tongue across his own behind narrow lips; he'd lost anything like normal human teeth but wasn't compelled to put them on display like that yet.

There's others on the battlefield, and she's drawing attention. The hound's making noise as it attacks, possibly to draw more of its kind on the new, obvious target the martial artist's made of herself.