Eh... y bueno, ahora estamos con Karla, con quien iremos a caminar y a pasear un rato.
Eh... and well, now we're with Karla, with whom we're going to stroll and walk around for a while.
Captions 20-21, Sevilla, España - Porteñas paseandoPlay Caption
Once again, quien is clearly acting as a relative pronoun, referring to "your cousin,"
and so is written with no accent over the e.
So what about cases where the sentence contains no noun or pronoun to which quien refers?
Quite often, this is a sign that an accent is needed. The most common case is when quién takes on the role of "interrogative pronoun," which, as the name implies, involves a question, as when the powerful and beautiful Julieta Venegas ponders:
¿Quién nos dice que la vida nos dará el tiempo necesario?
Who says that life will give us the necessary time?
Caption 3, Julieta Venegas - El PresentePlay Caption
And quién is utilized in indirect questions as well, as Juliana, back in Sevilla, demonstrates for us:
No sé quién irá a ver este video...
I don't know who will watch this video...
Caption 13, Sevilla, España - Porteñas paseandoPlay Caption
How would we treat quién if Julia were to have made her statement positive?
As it turns out, an accent is still required, even though most English speakers would not consider this an indirect question. You might look at this as a case where an indirect question is present, but it is being answered. The highly respected María Moliner dictionary calls this type of usage aclaratoria (explanatory). Note that there is still no noun or pronoun present to which quién is referring, so it is not behaving as a relative pronoun.
Like other interrogative pronouns, quién also retains the tilde when used in exclamatory way. (You will notice that these "quién" exclamations don't translate to English literally.)
¡Quién pudiera tener tus ojos!
If I only had your eyes!
¡Quién te escuchara todas las bobadas que estás diciendo!
If only the rest of the world could hear all the stupid things you are saying!
So, are there cases where quien doesn't relate to a nearby noun or pronoun, but still doesn't take an accent? Yes, when the "who" refers to some non-specific person, and so is taking on the role of "indefinite pronoun."
Quien mucho habla, no tiene nada que decir.
The person/a person who speaks a lot has nothing to say.
In this same vein, the phrase como quien means "like a person who" or "like someone who," sometimes best translated into English with "as if he/she [were someone he/she is not]":
Él contestó el interrogatorio como quien nunca hubiera conocido a la víctima.
He answered the interrogation like someone who [as if he (was someone who)] never had met the victim.
And, in another "indefinite" role, quien can also be used in place of nadie que (nobody that / nobody who) in phrases like this one:
No hay quien me detenga.
There is not anybody who can stop me. / There is nobody who can stop me.
[In English we can't have the double negative]