This is where the flashback starts, it seems somewhat abrupt to start in the aftermath, but we see everything up to this point, including the last meeting with Jagex's father and him stowing along at the end of War Arc.

We show Jagex (as a cub) standing in a valley of ash. The valley has been ripped apart and now it's covered in ash as far as the eye can see. Flakes of ash fall from the sky like snow. This cub is just staring blankly ahead at what remains of the valley, like he's in a trance. It's the basis of PSTD he'll carry around for the rest of his life.

He begins wandering, perhaps yelling out for help, asking if there's anyone left, maybe for someone in particular. He sees a glint of something in the distance, runs excitedly towards it. What he finds is metal armor half-buried in the ash, with a sword close by. It's the same armor he wears in the present. And in the armor is a wolf, or what was left of one, ash in the form of a wolf's body. The cub tries to pull the body up, but the ash crumbles underneath his paws. He watches as the wind carries the ash from his paws.

Maybe the cub starts to cry, maybe he's too shocked, or maybe he was crying the entire time. Jagex can't really remember. He remembers sitting there with the armor, just staring down at it in a daze for a long time. Eventually he hears someone approaching.

I feel like this character should be important, on either Weston's side (better) or Tairon's, and if this guy isn't developed here, he should be developed elsewhere in the story.

Gruff Wolf (off-camera): Are you Jagex of Tairon?

We then jump to Tairon's tower. Jaiwa (also a cub) is staring out of the window of the main room, this massive window that basically covers one of the walls and allows her to see the rest of the city below, Weston's army can be seen approaching in the distance.

A door opens and a Caretaker comes in with Jagex. He's still in a daze, he takes a few steps forward but before he can get very far Jaiwa runs over to him, hugging him and licking him all over. So many times that she has to stop to spit out the ash before licking him so more, leaving little streaks on his ash-covered face.

Jaiwa (crying, relieved): I thought I'd never see you again. I thought you were dead.

Jagex (vacant, abrupt): Father's dead.

Jaiwa (cringing from emotional pain): I know.

Jagex (vacant): They're all dead.

Jagex lurches forward until he's at the window, staring at the approaching army in the distance.

Jagex: We've lost the war, haven't we?

Jaiwa (sniffing): Yes.

Jagex: What happens now?

Caretaker (stepping forward): You will both be safe. There's no reason to hurt you now and Mosphet wouldn't dare if he has any hope of bringing Tairon back into the fold.

Jagex turns to look at her as she talks but he can tell she has something more she wants to say.

Caretaker (lingering): ...What happened out there, Jagex?

Jagex (deadpan): They burned.

Caretaker (not understanding): ...How?

A memory flashes back viscerally: a lone wolf covered in flames.

Jagex (disturbed, quiet, repeating): They burned...

Jagex turns back to the window and the Caretaker knows she's not going to get any more from him yet.

There's further conversation here where we can see the young Jaiwa and Jagex make a pact to fight for each other and eventually get revenge.