The Sky Blues have a powerful evil magic that could destroy the world, but Micael and Filla have a gem called the Moon Tear which can control the effects of the Sky Blues.
The current possessor of one of the Sky Blues, who has been corrupted by its magic, tries to kill Micael, but Filla stops him and they recover the gem. The Moon Tear does control its effects...but then it disappears. Now the two Sky Blues are sealed inside far-away temples in Heaven--apparently. In fact, Micael's deep blue eyes have a deep connection to the Sky Blues, and because of that, Baal keeps trying to corrupt Micael and use him to set free the sealed Darkness. However, for a few volumes Micael and Filla are happily unaware of all this. They have a few fun adventures and a few more serious ones...including Filla taking an accidental trip to ancient Japan and helping out a girl who's pregnant (and though she doesn't know it, the father is a dragon), and when Filla first kisses Micael, on Micael's 18th birthday.
Then Baal gets serious about his dark plots. Because of the deaths of two of the Diables who help to purify the negative energy in the world, the seal on the Sky Blues starts to break. The souls of the dead start becoming more and more restless, and everyone starts getting nervous. Micael is told that his eyes are calling the Sky Blues. Baal talks to him and makes him really depressed (which isn't too hard...), telling him that Filla abandoned him...Micael plunges into despair and self-loathing and stabs out his eyes with a sword. Then we get a long flashback of Micael's childhood...when it ends, we see that despite Micael's ill-advised efforts, he still has the Sky Blues within him. And the seal is about to break. Fortunately, even though one of the Moon Tears has disappeared, there were actually three to begin with...and one of the two that remains is Filla himself. (The one that disappeared actually represented Erinoa). And Filla has the potential to neutralize the Sky Blues.
Knowing this, Baal traps Filla in his castle... Micael goes to Hell, guided by Erinoa's soul, and he and Filla fight together against Baal and the magic of the Sky Blues. In the end, the Sky Blues are sealed within Micael and Baal is destroyed...or so it appears. Oh, and they kiss again. (No, I'm not going to keep track of every single kiss in the manga, but this was a really sweet part).
We're at the end of volume 8 by this point, which is a good place to stop if you can't buy the whole series at once.
[To be continued soon]