Disclaimer:: Don't own Shugo Chara!, never will. Peach-Pit is the rightful owner, so don't sue me. (-;
Hinamori Amu and Tsukiyomi Ikuto are two different people. They are polar opposites— Ikuto is playful and mischievous, while Amu is collected and in several occasions, wise for her age. They attract each other like magnets; even poles repel, while different ones don't.
Both realise this through time and they slowly —yet surely— start to get closer than they already are.
Their relationship begun as enemies, then acquaintances, which evolves to friendship, taking a step further by being lovers, and ending with being a married couple.
And they seal their relationship with an everlasting vow and a gentle kiss.