Learn Finnish: Nämä ovat ne roolit, joiksi opettaja meidät nimitti. - These are the roles as which the teacher appointed us.

The verb nimittää (to appoint or to name) requires the translative case to express what role or position someone is given. Because the relative pronoun represents the roles we were appointed as, it takes the translative form joiksi (as which).

Why is the pronoun joiksi in the plural form?

The relative pronoun joka always copies the number (singular or plural) of the noun it refers back to. Here, it refers to the plural noun roolit (roles), so we must use the plural translative joiksi instead of the singular joksi.

Why is the word for "us" written as meidät rather than me or meitä?

Personal pronouns have a special accusative form ending in -t when they are the complete object of an action. Because the teacher successfully finished appointing us, the sentence uses the total object form meidät rather than the partial, ongoing partitive form meitä.

Why is the word ne included before roolit?

While leaving it out would simply mean "these are roles", adding the plural pronoun ne (those) before the noun acts a lot like the English definite article "the". It emphasizes that these are the specific roles we are talking about.