Much of the appeal in Monster Girl Quest is some of the twisted horrors from Xelvy; monster girls are not always kawai, adorable bundles of fuck, sometimes they are terrible abominations with accentuated feminine features, or at the very least minimal possession of these features to be utilized for the purposes of wringing as much cum from the protagonist as they can; they are actually more Monster than they are Girl, but they are still monstergirls nonetheless.
I get the sense that unlike a normal monster girl, who'd surely consider you her (albeit largely unwilling) husband, who she'd cherish and protect from other monster girls, there is so little in the realm of love here with a creature such as this, her desire to capture and drain you is more akin to a predator like a mantis, her desire is instinctual and heartless, she'd likely never see the protagonist as anything more than a gradually replenishing semen tank.