Nociva is the feminine form of nocivo, meaning something (or someone) that is harmful, damaging or toxic.
Manuel Turizo sings "Lejos de ti, como si fueras nociva" to portray his lover as a negative influence he must escape from. It’s a vivid, less-common adjective that packs emotional punch and will stick in learners’ minds.
Manuel Turizo is here with a breakup song that's more about exhaustion than anger. He's walking away from a relationship that felt like a black hole. The opening line sets the scene perfectly: "Aunque está amaneciendo, todo se oscureció" (Even though it's dawning, everything got dark). He tried everything, but his partner was a constant source of unhappiness. He uses this great image of her being emotionally distant: "Tú siempre seca aunque afuera llovía" (You were always dry even when it was raining outside).
He admits that if it were up to him, he would have stayed. The problem wasn't a lack of love, but her unending sadness: "Pero siempre estabas triste" (But you were always sad). He even points out her "ojos rojos" (red eyes) weren't from smoking, but from crying. In the end, he had to leave for his own good. He says, "me tiraste al suelo y yo me recogí" (you threw me to the ground and I picked myself up). It's a song about realizing you can't fix someone else's sadness, and sometimes the only choice is to save yourself.