You're right, Sephiroth, he doesn't care. Or—well, alright. He's interested, but he doesn't know what the point of hearing about this is. It won't change anything to know what Sephiroth was going to do; the fact is that he didn't. Instead of abandoning Shinra and doing, presumably, the right thing, he did—all this other terrible shit instead. And he justifies it by blaming everyone but himself. Quite frankly, Cloud would call him weak to his face if he wasn't at least somewhat trying to keep the peace. He just focuses on his work, wending the roll of bandages around and around Sephiroth's body, tearing a piece off and clipping it, then starting on the next one. It helps to have something to do with his hands to focus on. He does look up, clearly listening, though.

That subdued interest is a little less subdued at the mention of Zack, naturally. It's really not hard to guess how to get his attention on any other average day, but he's especially vulnerable to it now. What question does he want to ask here to keep Sephiroth talking? he thinks to himself, and then immediately afterward has to marvel at the very idea that he wants Sephiroth to keep talking. He has literally never wanted that before. What the hell is going on in this world anymore?

"... What was he like?" he asks, eventually. With interest.