Yeah, the manga had some plot holes. I got the impression that Tsukune and the other girls end up getting into a polygamous marriage or something like Moka's father. I would have loved to see more of Akua's backstory. Did we ever get to see her birth mother? I mean, she is the eldest and it would have been interesting to see more of her childhood before she arrived at Moka's place.
Other than her original sister, we didn't. There was a small flashback of her and her sister (whom bore resemblance to Moka) in Hong Kong.
Spoiler ShowAlso a bit of backstory how she hated the human world, because the villagers caught her sister in suspicion of being a vampire and then just brutally mutilated her then impaling her severed body parts on display. That was a very dark and gruesome scene, I didn't even expected that kind of scene to be in a shounen manga.
There was no mention of her birth parents, Akua was just mentioned was
Spoiler Showa direct descendant of Alucard. Which was strange that even though that Akua was a direct descendant of Alucard, she didn't inherited the True Ancestor's/Shinso blood.
Also worth mentioning a funny scene with the Headmaster and Touhou Fuhai's bickering about them once flirting with Akasha, Moka's mom and how she would relentlessly beat them both up for their aggressive advances. And of course, my avvy, San Otonashi, it's a shame we didn't get to see the ship between her and Gin come into full circle. Though her character arc was quite memorable.