How does Unsouled end?

Lindon and Yerin fight their way free of Heaven's Glory, loot the School's treasure hall, and walk into a final ambush at the Ancestor's Tomb. Yerin defeats and takes in the Remnant of her murdered master, the Sword Sage, advancing to Gold, while Lindon survives Elder Whitehall's attack and throws him off a cliff. Together they fly out of Sacred Valley on a Thousand-Mile Cloud, and Lindon begins a discipline of his own making, the Path of Twin Stars.

How does Lindon beat Elder Whitehall at the end of Unsouled?

Whitehall corners Lindon at the Ancestor's Tomb and tries to destroy his core outright. Lindon survives by activating the Heart of Twin Stars at the final moment, splitting his core in two so that part of it outlives the strike, and Whitehall believes him dead. When Whitehall turns back toward Yerin, Lindon catches him off guard and drags them both over a cliff, saving himself mid-fall with the Thousand-Mile Cloud.

What happens to Yerin at the end of Unsouled?

At the Ancestor's Tomb, Yerin battles the Remnant of her master, the Sword Sage, and absorbs it, which pushes her to Gold and gives her a Goldsign — limbs of sword aura, shaped like blades. She then joins Lindon on his flying cloud, and the two leave Sacred Valley for the wider world. On the way out she tells him the truth that reframes his whole life: there is no such thing as an Unsouled, because the test only measured inclination, never worth or ceiling.

Why does Suriel save Lindon in Unsouled?

When the ascended Li Markuth slaughters the Festival and kills Lindon's mother Seisha, Lindon strikes at him knowing the blow is hopeless, choosing death over kneeling. That suicidal courage moves Suriel, the Sixth Judge of the Abidan Court, who freezes and rewinds time, revives everyone Markuth murdered, and has Markuth hauled through a portal to stand trial. She lets Lindon keep his memories and shows him his fated future, in which a Dreadgod destroys Sacred Valley and everyone he loves, telling him the answer is dedication. She leaves him a glass marble holding an ever-burning blue flame so she can find him again.

What does the ending of Unsouled set up for the rest of the Cradle series?

Lindon must climb past Gold and grow strong enough to stop the Dreadgod fated to destroy his home. The cosmic epilogue shows Suriel meeting the Judge Gadrael above a dying world and formally accepting the mission to retrieve Ozriel, the missing Reaper, without whom the Abidan cannot safely delete corrupted worlds. Lindon also carries treasures that matter later, including the Sylvan Riverseed, his future companion, and the series continues with Soulsmith.