This is the 1520th most frequent Japanese word.
セ
"セ" (se) is a katakana character used in Japanese, often representing the syllable "se" in foreign words, names, or onomatopoeia.
Here 'セ' is used to represent a sound or letter associated with summer imagery in Japanese poetry.
セとセミは夏の音の象徴と言えます。
The セ sound and cicadas are symbols of summer's sounds.
In this sentence, 'セ' is used as part of a repeated syllable pattern in a team name for stylistic effect.
その学校のチームの名前は『セセセ』です。
The name of that school's team is 'セセセ.'
Here 'セ' is part of the word 'セクシー,' meaning 'sexy,' showing phonetic borrowing from English.