尽 (Kanji for exhaust, use up)

Onyomi

JIN	We've exhausted all the GIN and tonic, go get more!

The rocker decided to chill out after he exhausted himself performing.

( を ) つ＊くす	to do everything in one's power , to exhaust every option trying to do XXX. ★★☆☆☆
( が ) つ＊きる	something is used up. ★★☆☆☆

理不尽(りふじん) な

unreasonable ☆☆☆☆☆
理 (reason) + 不 (un) + 尽 (exhaust, use up) = 理不尽 (unreasonable)

unreasonable, irrational, unjust