Fascinas is the 'tú' (you) form of the verb fascinar, meaning "to fascinate" or "to captivate". It's a powerful word that goes beyond simply liking someone.
In the song, the singer says, "Pa' que sepas que tú me fascinas" (So that you know you fascinate me). He's expressing that he is completely enchanted and captivated by this person, almost as if under a spell. It’s a romantic and intense way to describe a powerful attraction.
"Mami" by Los Primos del Este drops you straight into modern romance, corrido tumbado style. The narrator is head over heels for a girl, and he is not shy about admitting how much time he spends looking at her online. He opens with the ultimate compliment for the social media age: "Te ves mejor que en las fotos" [You look better than in the photos]. Whenever she posts, he is right there dropping heart reactions: "Cuando subes fotitos al Insta / Siempre te mando corazones" [When you upload little photos to Insta / I always send you hearts]. Here, "Insta" is just short for Instagram, and the diminutive ending in "fotitos" makes the scrolling feel casual and sweet.
Beyond the screen, the song turns into an intense confession. He repeats that she drives him wild: "me traes bien loco" [you've got me going crazy] and says "tu cuerpo me debilita" [your body weakens me]. He wants her all to himself without any distractions, begging "te quiero a solas" [I want you alone] so they can spend hours together. It is direct, affectionate, and relatable for anyone who has ever fallen hard after double-tapping on a crush's feed.