The relation between Mina and Akira is the most meaning and the most touching of the series. In my personal opinion, their bond is the reason why Dance in the Vampire Bund borns, because Mina wants to create a place in which humans and vampires can live together and the reason is that she likes humans, right? It's because Akira is with her. Akira is all for Mina. Her present, her past, her bond with life and with herself. He's the only one that she chose to stay with her since always, and she's natural just with him. Akira is who takes care of Mina, but she doesn't consider him just a servant, he's a friend, a lover, someone that doesn't think of her only like a princess but of a girl, of Mina.
When they were children Akira says to her

"I'll always be by your side, Hime-san"

and from that moment, until now, he's keeping his words, because even in difficult moments, he never leaves Mina's side, risking his life, risking his soul.
Akira and Mina are adorable together, I love their relation since the first chapter, when we can see the childish side of Mina, but even her sweet and kind words for him. She considers Akira precious and this is the reason why she brings a ring to him, that in a first moment is just stolen because Yuki-chan gifted it to Akira, but after that night, in which Mina constrincts him to sleep beside her, that ring becomes prove of Akira's loyalty and love for her. She doesn't intend to leave him to no one, and even if her finger is smaller to keep a ring, she always wear it as pendant, so it's prove of their bond.
Akira loves her with all the heart. He doesn't understand his feelings but it's obviously that Mina is special for him.

Akira is Mina's world, Mina is Akira's world

Many times, In the development of the story, their relation is ban from the others, and not just because Akira thought to prove something for his friend and classmate Yuki-chan, but because Mina isn't a simple vampire, she's the princess of vampires, a pure-blood one, and the heir of the prestigious and ancient Tepes family, that surely can't accept a werewolf as her husband.

She's trasgressive and her drem to live happily with the humans is coerent with her choose to love a werewolf. XD A werewolf that's servant of her family! XP
Mina doesn't take care of what's Akira is, because simply, he's the only one that can touvh her heart.
During the battles Akira and Mina remain hurted many times, but they always remain beside the other one. I love this side of them, their simply one of the sweetest couple I've ever seen and I'll support them forever!

When they're sad, they share sadness tearing, when they're happy, they smile together. It's splendid think that Tokyo, the city that Mina chose as place of the cohabitation of vampire and humans, is cradle of love for all the creatures that decide to own their own future.