Juntaría is the conditional form of the verb juntar, meaning "to join" or "to bring together". It translates to "I would join".
In this passionate song, Enrique Iglesias uses it to create a powerful and impossible image. He sings, "Por amarte juntaría la lluvia con el fuego" (For loving you, I would join the rain with the fire), expressing that he would do anything, even defy the laws of nature, for the one he loves.
Spanish pop star Enrique Iglesias goes all in on pure romance with "Por Amarte". Right away, he tries to pin down what true love feels like, calling it a rare, once-in-a-lifetime miracle that completely scrambles your routine. He describes those exact physical reactions you get when you have a massive crush: your mind races wondering where she is, and the second you see her, you get nervous ("te pones nervioso" [you get nervous]) while completely losing track of time in a hug ("te olvidas del tiempo" [you forget about time]). He also points out that real love is steady; it is not a "viene y va" [comes and goes], which is the Spanish way of describing something fleeting or inconsistent.
Once the chorus hits, Enrique tosses realism out the window and dials up the drama to maximum volume. To prove his devotion, he promises impossible, fairytale feats: he claims he would steal a star out of the sky ("robaría una estrella" [I would steal a star]), cross entire oceans just for a hug ("cruzaría los mares" [I would cross the seas]), and even make rain and fire mix together ("juntaría la lluvia con el fuego" [I would join the rain with the fire]). It is grand, slightly over-the-top, and unapologetically sweet devotion.