A Yojijukugo (四字熟語) is a unit of four kanji characters that usually represents an idiomatic saying in Japanese. It is itself a yojijukugo, even though it isn’t idiomatic, since the term can also broadly refer to a non-idiomatic phrase of four characters.
Shunkashūtō (春夏秋冬) is a nice one that means the four seasons of the year, and so is a fourfold written in four kanji characters.
Eshajōri (会者定離) is hopefully appropriate, meaning “every meeting must involve a parting”.
Further Reading:
https://en.wikipedia.org/wiki/Yojijukugo
https://en.wikipedia.org/wiki/Shunkash%C5%ABt%C5%8D
https://www.tofugu.com/japanese/yojijukugo-idioms/
https://www.nippon.com/en/nipponblog/m00111/
https://en.wikipedia.org/wiki/Japanese_proverbs
And these are just interesting:
https://en.wikipedia.org/wiki/List_of_kanji_by_stroke_count
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