Asspull: The existence of aliens as a fourth faction along with GM, the dhampirs and Akibara could be seen as this though it was made obvious that there was some sort of force affecting GM. Stella being Saberhagens daughter could also be seen as this.
Marty Stu: Akabara was an all powerful vampire, never fully losing a battle as a great general super charismatic with three woman practically in love with him and he was even immune to sunlight to boot. As the events of the manga in the present day show, this didn't work out too well for him.
Akabara is actually a deconstruction as it is his Marty Stu traits that turn everyone against him and condemn him to several millennia of suffering because he's too damn good at everything. To make matters worse, his ridiculously selfless personality keeps him from taking the easy way out, even though he's clearly Too Good for This Sinful Earth, so he continues to play the bad guy to ensure that his enemies don't turn on each other.
Squick: Akabara and Bridget's relationship in the past. Having adopted her when she was 10, he genuinely considers her his "cute daughter" and treats her like his little girl, sleeping in the same bed, bathing with her, letting her sit in his lap, etc; but in most of the flashbacks, they look to be the same age.