Inalcanzable means 'unattainable' or 'unreachable', a perfect word to describe someone who seems out of your league.
In the song, Kali Uchis sings about an angelic woman who is a 'princesita inalcanzable' (an unattainable little princess). This powerful adjective paints a vivid picture of someone who is so special they are almost untouchable, setting the celestial tone of the song.
Kali Uchis and Peso Pluma team up on this smooth R&B track to celebrate someone so pure and untouchable they feel celestial. While everyone else chases money and fame with "un amor superficial" [a superficial love], this girl only wants "calma, no dañar su alma" [calm, not to hurt her soul]. The lyrics say people made big promises and broke her heart ("le rompieron el cora'"), leaving her with dry eyes from all the crying. Even so, she keeps smiling. She simply lives on a higher plane where bad energy cannot touch her: "Heaven's her residence, y ella no se va a caer" [and she is not going to fall].
What makes the song fun is how playful the praise gets. Instead of wallowing in heartbreak, the singers crown her "la favorita de Dios" [God's favorite] and treat her like a rare prize that regular people cannot afford. The slang adds real flavor here, like shortening corazón [heart] to "cora'" or calling an out-of-reach woman a "princesita inalcanzable". In fact, Peso Pluma basically tells anyone hoping to date her that they better start praying: "El que la quiera, que rece" [Whoever wants her, let them pray]. She is light, she is an angel, and she knows it.