First glimpsed in good light on Coda: a delicate lacy dress with three or four shawls wound around her shoulders, waist, and wildly curly hair — though, being a shape-changer, even this may be a chosen look rather than an innate one. Her voice is exclamatory and mannered, fond of grand words ("lamentable," "pernicious") and endearments ("my dear, sweet Eira," "my darling Hugo"). She reads the world through romance, and actively engineers it.
In Triage, Vesper is offstage at a concert, matchmaking two of her friends, when Hugo reaches her about a suicidal stranger he doesn't want to handle alone. She agrees to help. Flash Fire opens in her voice, mourning that the matchmaking has just failed — she had spent months posing as a barista to engineer it — before she takes Eira's case. She translocates ("pops") to Hugo's side in Oxbow, meeting him in person for the first time on the page, comforts Eira, joins Eira's hand to Hugo's, and moves all three off-planet to Coda. There she sets them down carefully at the edge of the terminator band to avoid the Consortium's surveillance, then goes quiet.
She returns to narrate Right Hand Man in her own voice. Back on Vellum consoling her old coworker Cariad, she pops over to Eira's new Coda house to angle for the group's next destination — the silica planet of Threnos, where her friend Clara lives. Her real aim is matchmaking-as-strategy: pair Eira with Clara so Eira becomes "a permanent fixture," and Hugo, for once, doesn't drift away. And it's her memory that hands us Hugo's one near-friendship — the doomed revolutionary he walked away from — which she now watches for signs of repeating.
Vesper is a node like Hugo, designated 02 to his 03 — both of them members of the Array, the small set of designed beings the story finally names in Overtones. She can translocate between planets with some preparation — and, notably, she's the only one of the pair who can; Hugo gets around the slow way, by cruiser and star bridge (she once left his stranded on Caligo). Unlike Hugo, she is attuned to reading organic neurons, one of the story's hints that each of these beings has fixed, particular gifts. She's also a limited shape-changer — "by no means an emulator," but she keeps a saved "form" for each world she frequents (defaulting, on Caligo, to her "Codan form"), and scatters into a cloud before she pops so she can settle into a shape as she arrives. Where Hugo dismisses mortals as "non-entities," Vesper insists on seeing them as whole people.