Immortal Regis and its sequel Cavalier of the Abyss
Human/Demon love
thought its the opposite they start as Master/Slave and progress to friends and potential lovers
and when you thought its all merry they become intimate bitter Enemies
will there be ever a happy ending!?

I forgot to mention
Cannon God Exaxxion
the Aliens her are not one dimentional and there is also interspecies love and NTR
the main char grandfather is one case of magnificent bastard that at sometimes can be as rage inducing as the Aliens