You all can see how their relationship is peculiar from the first episode. They are “family”, and this theme will always be there, from the beginning to the end. From the start, they will protect each other, and act consequently thinking only to the other's happiness!

While they live under the vampires “protection”, Mika is like the “mother” of the family. In the name of the love he feels for Yuu and the other family members, he is willing to suffer for the greater good. In fact, he will go to the extent of giving his blood to one of the high-ranking noble vampire, only to guarantee his brothers and sisters food.

Yuu, seeing how Mika is so willing to sacrifice himself, gets mad at him. Yuu is hot-tempered, and yet very shy, so he won't admit he is just worried about him. He will just shout at his face. However, Mika knows Yuu! That's why, in those moments, he will cheer him up by showing him the upside of being together, as a family!

The last sequences of the first episode are a crescendo of tension. Mika and Yuu, together with the others, plan the escape, but are discovered by Ferid Bathory. One by one, their family members are brutally killed right before their eyes. Mika tries to shoot at Ferid Bathory, only to give Yuu a chance to escape, but ends up with an arm slashed and a hole in his chest. Rage takes over Yuu, as he takes the gun and shoots at Bathory's head. Right after, the moment when Yuu will try to take the agonizing Mika outside with him is one of the most touching part. Mika, who sacrificed everything to save Yuu, will ask him to escape and not to let their death be in vain. Their paths separate. Alone, with the dream of hope that he and Mika shared fallen to pieces, Yuu swears revenge towards the vampires!

Now on one side there's Yuu, saved by Guren – Lieutenant of the Moon Demon Company, opposing the vampires. Yuu is destroyed by his family's death, and will devote himself to the training. Yuu's hope is to, someday, make the vampires pay for the future they took away from Mika and the others.

On the other side, there's Mika, saved by a powerful vampire – Kurl, the vampire queen of Japan. The cruel fate will strike him, as he will be turned into a vampire. From there onward, Mika's purpose is to find Yuu and reunite with him. So as the years will pass, they will only think of their own purposes, and act consequently. Basically, they are each other's reason to keep on living, and they cling to that reason with resolution!

Mika and Yuu are like black and white. It's interesting to see how they evolve and change, and how their tragic past changes them.When they were little, Yuu was a hot-tempered, stubborn kid who had always something to say. In those moments, the sweet Mika tried to cheer him up, or make him calm down. Yuu was usually a pessimist, and in those moments, Mika's kind and upbeat character was essential to soothe him.

Years after, the tables turn. Yuu, who initially was so negative, becomes a person who is able to make friends and even to cheer them up. He finds a new “family” in his team, and all the pain he felt for Mika's loss becomes the strength that will help him make the right decisions, as he doesn't want to lose his dear ones anymore.

Now a vampire, Mika, who was so cheerful and optimistic, becomes cold and cynical. The injustice he felt in the past, for being turned into a vampire, and for being separated from Yuu, have hardened him. With these changing, their meeting after a long time shows you how different they became, and yet how one needs the other to keep himself together!

What made this couple become canon, though, is the way Mika and Yuu express their feelings for each other. Their bromance is more than bromance, and yet less than romance. It maintains the right balance that makes the girls go all soft, and yet allows the boys to like this show anyway.

They just feel that they can be themselves when they're together, and when they meet again after years, Mika will cry, while Yuu will be so shocked that he will turn into a demon. Only Mika's words will save him, once again.

Later, the moment when Mika, on the verge of death and unwilling to save himself, will be constricted by Yuu to drink his blood, meaning that he will turn into a real vampire with no turning back, will give you moments of real, much appreciated bromance. Mika is afraid that Yuu will hate him, but Yuu assures him that he can never hate his Mika, because Mika, human or vampire, will always be Mika. Tears, hugs, sweet words and then Mika finally drinks Yuu's blood, becoming a real vampire!

The surprise in discovering that Mika is still alive makes Yuu so happy that he will allow himself to cry. Seven days after the battle, when he wakes up in a hospital and remembers what happened, he realizes that his teammates have made it back alive as well, he bursts into tears, to the joy of Shinoa who teases him non-stop.

Mika, on the other side, is just as happy to have found Yuu. Their meeting was by chance, but the only thing that really matters is that they can reunite, and the dream of hope they had when they were little, can be put back together.

In that moment, their willing to save each other strengthens. As they think of each other at the same time, while watching at the moon, they swear to save the other, at all costs! After Yuu realizes that Mika is still alive, his way of acting will revolve around the sole purpose of taking him back, and the same goes for Mika. Both lead by the thought of the other, they'll finally meet again and have a chance to catch up a bit of the time they lost.