Amarrándonos comes from the verb amarrar, meaning 'to tie' or 'to bind'. The -nos ending makes it reflexive, meaning 'tying ourselves' or 'tying our hands together'.
In the song, Carlos Rivera sings, "Y vamos amarrándonos las manos y así no te vayas, no." This line beautifully conveys a desire for an unbreakable bond, a playful yet profound commitment to stay together, making it a unique and memorable word choice.
"Serás" is Carlos Rivera's vow of steady devotion. He opens by inviting a partner to co-write a shared future together — "Vamos a escribirnos una historia para ti y para mí" [We're going to write a story for you and me] — then spends the rest of the song naming exactly what she'll become to him no matter what comes: "Serás mi compañía, en este invierno mi calor" [You'll be my company, my warmth in this winter], his joy, his courage in the fight. It reads less like a song about feeling and more like one about function — she's cast as the one constant that gets him through winter and war alike.