1An older brother; used familiarly (reading にい) to refer to one's elder brother in casual speech.
にい、今日の宿題を見てくれない？
Hey, big bro, can you check today's homework for me?
子どもは兄のことを『にい』と呼んで慕っている。
The child affectionately calls his older brother 'nii' and looks up to him.
あのにいはよく近所の子たちと遊んでいる。
That older boy often plays with the neighborhood children.