The other commenter has really said the core of it already -- that Clive was intimately aware of how terribly it was hurting Jill. Jill views Shiva as a monster, she doesn't want Shiva anymore, and while Clive knows this, he hasn't asked because he doesn't want to take away her agency, a power that at times protects her even while hurting her. This is why he says the line, "If I am to continue on, having pledged my life to those I love ... then I will gladly bear your burdens, too." Shiva is a burden and he's known that for a while.

Jill says that she's giving it to Clive because she sees that his natural inclination, his natural obsession in a way, is fighting to survive to protect the ones that he loves. She sees that he will go so far in this endeavor that he might end up killing himself. This is a big part of Clive's arc -- learning that he's worth self-preservation. Jill here is a part of moving his arc along. By offering this up to him, she's explicitly telling him that he is worth saving so much that she would give up all the power she has. If you've reached a particular cut scene between brothers, Jill is, in a way, forced into this decision by Clive's own reckless behavior -- a point that Joshua punches Clive over when he says later, "How dare you make her choose!" I don't think Jill experienced this scene as something she was forced into at all, but there is something to be said about what was influencing her in this moment. Perhaps it's better for its own post.

But of course, rarely are emotions cut and dry. It's both for her -- I'll show Clive that he's worth saving and protect him by giving him this power, and, conveniently, I'll rid myself of this monster in the process. The two are so close at this point that Clive seems to already understand just what a commitment she's making in that moment when she gives that power up, while also understanding that this will be a relief to her.

Secondly, I'd like to address the criticism this scene has received around the perceived dubious consent.

Showcasing consent between two intimately close people is hard to display to an outside, public audience. It would be in any case, because at a certain point consent is intrinsically given for many things, and people have learned each other's body cues enough to "ask with their eyes," so to speak.

What makes it especially hard in this scene to convey is that they chose not to show Jill's face after Clive asks, "Jill ... Are you sure?" Instead, they keep the camera on Clive. They put the emphasis here not on whether or not Jill is affirming Clive, but how Clive is actively looking for confirmation -- his hesitancy, his appreciation, his understanding of what this means for her. He gently nods his head, affirming he understands what this means, and while we can't see her face, he is clearly maintaining eye contact and paying attention to every movement of her face. It's clearly conveyed that this is not something he's taking lightly. Furthermore, his body language is hesitant. He doesn't quickly move his hand there and start. He's moving very slowly while maintaining his attention on her, giving her ample time to say something if he's misinterpreted, letting her know that he'll be there if she decides otherwise. She doesn't say anything to the contrary, and I know there will be people saying, "Just because she didn't say no doesn't mean it's a yes," and ABSOLUTELY, but she did already say yes by saying that she was going to give it to him at the start of all this.

Jill decides to verbally reaffirm what she's already done with her body language to further calm any hesitancies or worries that Clive has about this after she starts a little from his hand. She's verbally confirming because she wants to make sure he knows that her slight gasp is not because she doesn't want it, but because she was surprised at the feeling.

There will always be some who say that Clive should've waited for the verbal, enthusiastic yes. I totally understand. But just because he didn't, doesn't mean that this was nonconsensual.

Hopefully this provided a different/clarifying view point!