The serum is a relief in more ways than one, and Jayce is hopeful when Alucard injects it that it will do exactly as it does. Whatever power the Hexcore has, it hasn't been able to become as powerful at manipulating Viktor as it may have in their world. The many ways in which they have planned this is why it is going to work, as it never could have in Piltover.

Jayce is glad the runes are finished before he had an ability to think about what he was doing. Focusing on what they need to get done matters more than him being squeamish. He pulls the lever, crank it, like they've said before and now, but it will be the piece that matters here. Everything to this point was to keep him alive, and this is the defining moment.

He turns his attention back to healing, making that his entire focus from now on. Jayce pours his magic into Viktor's both on top of the serum to try and boost his life force, not caring if it bleeds his magical endurance to the very end of it. They're in the end zone now.