Dark Angel - Futa Monster Girls, #7

There is no resting in the fighting against evil, and Alina has never been one to turn her back on the action. Being a dark witch, most looked at her as a demon's spawn, but she didn't let it bother her, doing her best. That was why she joined Anton and his band of adventurers in their fight against Thornhill, the necromancer. Now, after months of pursuing the dark wizard, they finally tracked him to a mysterious dungeon on the Adventure Belt, and yet, they seemed too late to stop him from activating a strange relic and opening a portal to the dark void.
What came out of it, none of them was expecting. It was an angel. There was something wrong about the monster girl, though. Something dark, dangerous, and corrupted, and it didn't take long for calls of action against that otherworldly being to be sent, though Alina wasn't sure that was something they should do. And so she went to the monster girl, never expecting that it would lead to the romance of a lifetime.