Nano

This character overuses or overemphasizes the word "nano" at the end of their sentences.

Sometimes appended with "desu" at the end.

"Nano" or "no" at the end of a sentence is the formal equivalent (and somewhat feminine) to putting "~n desu/da" pattern. In simple terms, "nano" is used to place emphasis on what the speaker is saying.

In fiction, immature / childish characters are prone to this pattern.