The only lingering issue that bothers me is the unknown fate of Kona's mother.

I still enjoyed the hell out of it. Aki and Kona were great characters, even though I hated the latter at first.

The thing about Kai being a total asshole at first is alleviated by the fact that he does one thing without fail: protect's Aki's happiness. He's loved her since they were kids, and protects her at all costs when it counts. Most of his actions were to keep her from ever getting upset or sad. He was hopelessly devoted to Aki and Aki alone. He might try to play being aloof from time to time, but Aki's happiness always came first.

Helping out Kona was just a side-thing. Still, I doubt she'd be that upset being relegated to his mistress. Aki probably would object though, so Kai would follow her lead as always.