Curate, connect, and discover
Ekko arrives a bit earlier just as Jayce is shooting Viktor in the chest. Jayce gets sent back in time somehow from the combined power of the Z-Drive and the Commune's collective death.
Jayce's consciousness rockets back in time and splices with his younger self just as he's finished 'negotiating' with Silco. Still reeling from his Arcane induced-trauma and killing his partner as well as who knows how many people by proxy, he arrives half feral and about 99.7% convinced he's either hallucinating or in Runeterra's version of Hell.
Jayce, canonically suicidal, Talis comes to the conclusion that he needs to blow up the Hex Gates and that the resulting explosions will either jar him out of his hallucination or finally put him out his misery and let him join Viktor.
Unfortunately, after months spent in isolation in an apocalyptic future, Jayce has gained an unfortunate habit of talking to himself as he figures out problems.
And Silco has been standing there the whole time.
Silco reiterates that he's not going to give up Jinx and Jayce just goes 'I don't give a fuck about her anymore' and attempts to leave.
Silco is absolutely befuddled by Jayce's complete personality change, but refuses to show it. After raising Jinx, he's learned a few methods for bringing people back from the edge. And considering his investment in getting access to the Hex Gates, he is very unwilling to let Jayce just walk away.
Especially when Jayce mentions he's supposed to be dead.
----
Silco convinces Jayce he'll need an explosions expert and that he'd never be able to blow up all the Hex Gates by himself. Jayce holds resentment for Jinx blowing up his partner and pseudo-sister's mom but had calmed down enough to realize that if he was in the past, it would be better to be close to Jinx and prevent history from repeating itself.
Cue Silco and Sevika having to wrangle Arcane-ified Jayce and Shimmered Jinx and prevent them both from causing Hexplosions.
Jayce, dis-illusioned with the Council, decides it would be faster to just pull a Viktor and 'not ask for permission' before destroying Hextech. He tells Silco that if he's willing to help destroy the Hex Gates, he'll give him his nation of Zaun -- and pardon Jinx.
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Elsewhere, in Piltover, Viktor has collapsed in the lab and entered a coma. There's a strange pattern on his chest and back. Almost as if he'd been shot with a very powerful energy blast from a very large hammer. But no injury, it was as if it had already been healed.
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When Jinx kidnaps Cait and Vi, Jayce is the one to ask her to spare Cait and let her leave. But also, the one to stop Cait from shooting Jinx.
"Stand down, Sprout."
"What are you doing! She's killed people Jayce."
"So have I. And I need her." Jayce is still suffering hallucinations and time-travel-induced jetlag, so in the tense moment he forget when he is and admits to killing Salo and blowing a hole through Viktor's chest.
Caitlyn is more shocked by the latter, "You-you killed Viktor?" She liked Viktor as a friend, they got along despite their differences. "Why? Why would you do that!"
Jayce, dissociating and in complete sincerity, "Because I needed to save him."
Following that insane response, Jayce slowly walks toward Cait with a pleading look in his eye, "Jinx is going to help me destroy HexTech and then we can save everyone. And then I can focus on curing Viktor!"
Cait looks into Jayce's -her brother's- eyes and understands Vi a little bit more, her desperation to see the good in Jinx.
Caitlyn can see her brother in this stranger's eyes, but he feels miles away. She has no idea how she's going to reach him.