Soy tuyo
, chica (I'm yours
, girl)
Mi chica
, yo soy tu hombre (my girl
, I´m your man)
"Tuyo" and "tu" have the same differences than "yours" and "your".
When one writes a pronoun in Spanish, is either to add an emphasis on the sentence or to avoid a possible subject confusion.
In this case, it is a "possessive" emphasis: I
am your man, no one else is (or can be).