The Hades Calculus. Gunmetal Olympus, #1

Decadent cyberpunk cities. Greek mythology and giant mechs. Hades and Persephone as never seen before. For generations, colossi have besieged the gates of Elysium. Each day, the city's fall looms closer. As one of Elysium's rulers, Hades has long sought to break this stalemate. In Persephone, a cyborg tailor-made to kill, she finds the key to victory and the perfect pilot for her war machine. She will acquire Persephone at any cost. Born to wield violence and with the bloodthirst to match, Persephone chafes under her mother's control.
At the first opportunity, she brutally breaks free and seeks sanctuary with the unlikeliest of patrons: the Lord of the Machine Dead, the Master of the Underworld.  All Hades and Persephone have to do to realize their goals is to navigate the city's treacherous politics-and survive the coming war.