我D世界只有他我D世界只有她
[wŏ d shì jiè zhĭ yŏu tā wŏ d shì jiè zhĭ yŏu tā]
Here, 'D' is used instead of the word '的' to add personality in a cute or colloquial way. This username indicates an exclusive affection towards someone—either male (he/him) or female (she/her). The user expresses devotion to this single person, suggesting their whole world revolves around him or her.