This might depend a bit on which 'first binding' you're talking about, as folks sometimes use it differently. I'm assuming you mean that first set of folks in 'The Atlas Six'? The core group is obviously the six new Magicians: Libby Rhodes, a powerful physic theorist who feels the pressure to be perfect, and her rival Nico de Varona, a natural talent with a chaotic charm. Then there's Parisa Kamali, a telepath who basically weaponizes intimacy, and Callum Nova, who manipulates emotions. Reina Mori is the naturalist, incredibly grounded and in tune with life forces, and Tristan Caine can see through any illusion.
They're all brought together by Atlas Blakely, who runs the Alexandrian Society. The dynamic is less about a single 'protagonist' and more about this volatile, fascinating ensemble. Honestly, Parisa and Callum's morally gray games often steal the spotlight for me, even though I'm more drawn to Reina's chapters. It's the friction between them all that drives the plot forward, especially the simmering tension between Libby and Nico.