Black Bird, Kamisama x Oresama x Dannasama!? Recommendations
In both mangas, a girl and a deity (well, demon in Black Bird) make a promise to marry each other in the future. When the female turns 16, the male goes to retrieve her, but the girl is reluctant to marry him. However, the girl starts falling for him, but their may be many obstacles that stand in their way for their relationship to thrive. Both males in both mangas are strong, and more powerful then others.
If you like romance, supernatural titles, and enjoy shoujo titles then these two mangas would be perfect for you (however, Black Bird is a bit smutty)