Learn Finnish: Uusi lempinimeni on Karhu, koska ystäväni kutsuvat minua Karhuksi. - My new nickname is Bear, because my friends call me Bear.

This showcases the rection of the verb kutsua (to call). When you call someone by a name or title, that name must be in the translative case (Karhuksi). In the first clause, it is a basic "A is B" sentence (My nickname is Bear), so Karhu stays in the nominative case.

Why is the word for "me" in the partitive case (minua)?

The verb kutsua requires its object to be in the partitive case when it means "to call someone by a name". So, the person being called takes the partitive (minua), and the name they receive takes the translative (Karhuksi).

The word ystäväni can mean "my friend" or "my friends". How do we know it is plural here?

We know it is plural because of the verb kutsuvat (they call). When adding a possessive suffix like -ni to a nominative plural noun (like ystävät), the plural -t marker is dropped. This makes the singular and plural forms of ystäväni look completely identical, so you have to rely on the verb to find the number.

Does the verb kutsua always use this partitive plus translative structure?