The Undercity, where he's from. He swore he would make things better for them using Hextech.

[ Jayce doesn't have to think about this, he knows exactly why Viktor wants to go back and that he will have a hard time letting go of it. He probably would put his life at risk out of sheer stubbornness. Jayce was always happy to work with him in designing new Hextech for the common folk, and yes, of course for the Undercity, but he never understood the depth of it. ]

Everyone has failed the people there. He doesn't want to. If he forces me to go back, I'll do it for him after he dies.

[ It's a lose/lose situation for Jayce and he knows that. It's upsetting, for certain, but he also sounds just wearily accepting of it at the same time. That is a fight he and Viktor will have to have someday, and he already knows how it will all go. ]

I'm sure there are other immortals or long-lived people who were Summoned, you should ask around. Make a club.

[ He smiles, teasing. ]