Rehén translates to "hostage". It's a striking and somewhat unexpected word to find in a romantic song, making it particularly memorable.
In the lyrics, the phrase "Nos tiene de rehén" (It holds us hostage) is used to describe how love has completely taken over the protagonists. It powerfully conveys the idea that their love is so intense and inescapable that they are entirely at its mercy, unable to break free from its grasp.
"Perfecta" is about a friendship that turns into something more. The narrator falls for a close friend, and even though they both know getting involved could ruin the friendship, they go for it anyway.
The chorus is a simple, direct declaration: this person is all they need, and they would love them for as long as it lasts. The verses fill in the story - the narrator never believed in love at first sight, but after finally giving in, they realize their friend is exactly what they always dreamed of.
It is a sweet, upbeat song about taking a risk on someone you already trust, and having it turn out to be worth it.