The word "tattoo" is a direct loanword from English into Spanish, making it immediately recognizable and intriguing for English speakers.
In the song, the artist sings "Hoy me hice un tattoo que dice solo 'tú y yo'" (Today I got a tattoo that only says 'you and I'). This word is central to the song's theme of eternal love and commitment, as the tattoo symbolizes a permanent declaration of affection. Its familiarity combined with its significant meaning in the lyrics makes it a compelling choice.
The title is a pun. Tatú sounds like "tattoo", and the tattoo is the whole point. María Becerra spends the verses on how fast it happened, "En poco tiempo te adueñaste de todos mis pensamientos" [In a short time you took over all my thoughts], and then does the least reversible thing anyone can do about a feeling: "Hoy me hice un tattoo que dice solo 'tú y yo'" [Today I got a tattoo that just says 'you and me']. Ink instead of a promise.
Everything around that line reaches for something that will not expire. The first kiss was "como salido de un cuento" [like something out of a story], one "del que nunca despierto" [that I never wake up from]. She and XROSS trade verses about going back "un millón de años luz" [a million light years], and the only condition she can think up is the end of everything: "Y si se acaba el mundo quedaremo' tú y yo" [And if the world ends, it'll be you and me left]. By the outro the song has worn down to the two words on her arm, "Tú y yo, tú y yo, tú y yo" [You and me, you and me, you and me], repeated until it sounds less like a wish and more like a fact.