I'm Not The Final Boss' Lover Vol. 4 (novel) - I'm Not the Final Boss' Lover, #4

A corrupt hero. An overprotective duke. A stalwart maiden. As the demon lord's arrival draws near, Jun and the Dark Knights became busy preparing for it. However, brewing trouble puts their plans in jeopardy: Fabian, once Jun's ally, has finally accepted that Jun won't be returning to his side, which now makes her a hindrance to his schemes. Despite their differences, the two competing corps are tasked by the emperor himself to clear a dungeon side-by-side.
As a result, Jun and her allies must keep their guard up-Fabian's cunning and thirst for power may lead to their downfall if they're not careful. But Fabian isn't their only enemy. The Dark Knights discover they have more foes than they thought, and at the core of this sinister web lies the person who betrayed Mayer during the first playthrough. Can Jun and her allies stay alert to the dangers that lurk in the shadows? And will they be able to hinder Fabian's lofty ambitions? In every RPG, you must choose your allies carefully.