Readers of the first novel in the series, The City We Became, have already met Padmini Prakash. She loves pure math and hates New York City, but due to familial pressures is preparing to be a Wall Street "quant". (Oh, she has also been personally chosen by the borough of Queens, NY as its human avatar.)
She plays a larger role in this sequel, which according to Aidan Tompkins, qualifies it as mathematical fiction:
Contributed by
Aidan Tompkins
Readers of speculative fiction know that it's worth finishing a series for the finale, and that is doubly true for the Great Cities duology. The second book has even more math concepts than the first to think about, where the character that uses magic math has a major role. Padmini starts as a grad student in New York, where The World We Make mainly focuses on a large cast of characters that represent different cities. Padmini channels her "city magic" by imagining constructs from math, and I'm a sucker for badass equations. In many ways, it's similar to the parts I like from Middlegame, including highstakes action with problem solving in parallel universes, and I even preferred the execution of the magic math in The World We Make! Padmini has enough social skills so she doesn't fit into a savant pigeonhole, even as the aro/ace member of the LGBTQIA cast. The references to "nonEuclidean geometries" are a little more accurate than Lovecraft, at least, and the other descriptions of the quantum multiverse are surprisingly coherent. At least, it made sense to me even though I'd never heard the word kugelblitz, so I recommend everyone listen to the audiobook with all its fourthwall breaks and creepy sound effects!

(quoted from The World We Make)
"There are no equations for the math of the multiverse, other than the tentative ones she has begun to develop from looking at patterns in the raw coordinates, but...
The coordinates are different." 
(quoted from The World We Make)
"Oh! what is math to her is art to himbut there's not as much daylight between art and math as most people seem to think." 
(quoted from The World We Make)
"Life runs on chaos math." 
