김성준이

In a sentence

• 김성준이는 축구를 잘합니다.

  Kim Sung-joon is good at soccer.

  Here, '김성준이' is used as the subject of the sentence, denoting a proper noun referring to a person's name.

• 내 친구 중 한 명이 김성준이야.

  One of my friends is Kim Sung-joon.

  In this sentence, '김성준이' is utilized as a complement of the predicate, connecting the subject to its description.

• 김성준이로 말할 것 같으면, 그는 정말 친절해.

  Speaking of Kim Sung-joon, he is really kind.

  Here, '김성준이' is used as a topic phrase introduced by '로 말할 것 같으면,' emphasizing discussions around him.