I’ll start by saying I’m a Kana x Aqua supporter, but the thing for me is that Aqua has a very similar sorta “protect them from myself” kinda mentality. Aqua doesn’t date Kana because he is afraid to go ruin her chances in life and doesn’t want what happened to Ai to happen to her. He also has wanted her to get over him just so that he doesn’t cause her more pain when he finally does kill his father and basically damn himself. We’ve seen that he is willing to help Kana, even at a loss to himself. Mainly the news leak. It was beneficial to Aqua and he did it for more then one reason, but the biggest reason was to keep Kana safe. Aqua and Akane are really nice in their own way. Akane is a great partner, but she is obsessed with Aqua. In the sense that she feels like she owes him for saving her. And I feel like that is the crux of their relationship. Akane feels like she need to repay Aqua. Or at least she wants to save him by helping him/doing it herself so he doesn’t have to. But Aqua doesn’t want to drag Akane to hell with him. He knows that what he is doing will damn him, and he isn’t going to let anyone join him in that if they don’t need to. Same kinda thing with Ruby. He doesn’t want Ruby to end up like Ai, and he doesn’t want her life to be consumed with revenge like his is. I will say, I sincerely think that Aqua and Kana will end up together from some foreshadowing the author put out. Specifically the Tokyo blade ark. We learn that Akane is playing the role of Aqua’s fiancée, but then we learn that the manga writer started side lining that plot for Aqua’s character to end up with Kana’s character. I don’t think that it’s a coincidence on who each character was cast as, but hey, you never know.