Cereza literally means "cherry". It's a sweet and evocative word that stands out in the lyrics.
In this song, Manu Chao uses "la cereza con esa gran fiesta" (the cherry with that great party) to symbolize the best part, the highlight, or the finishing touch of something wonderful. It's a delightful metaphor for what makes life or a moment truly special and worth savoring.
Manu Chao's "Me Quedo Contigo" is a really sweet song about choosing love above all else. He starts by saying, "soy un hombre perdido si me das alegre" [I am a lost man if you give me joy], which is a bit of a funny way to put it, almost like joy makes him lose himself in a good way. He talks about being free and giving, but then he brings in this idea of a "cereza con esa gran fiesta que lleva consigo" [cherry with that great party it brings with it]. It sounds like he's saying that life can be a big party, but there's one special thing, like a cherry on top, that makes it truly wonderful.
That special thing, of course, is the person he's singing to! He makes it clear when he says, "si me das a elegir, me quedo por ti" [if you give me a choice, I'll stay for you]. It's a simple, direct declaration of love. He even mentions wanting to be "a su lado" [by your side] and seeing "soria con tus ojos" [Soria with your eyes], which could mean he wants to see the world through their perspective, or perhaps Soria is a special place for them. Even if things lead to "el olvido" [forgetfulness], he's not giving up, because for him, being with this person is what truly matters.