The kanji 亥 represents the twelfth and final sign of the Chinese zodiac, corresponding to the year of the Boar/Pig. It also signifies the time period of 9 PM to 11 PM. It's often associated with darkness, completion, and the end of a cycle.

・On-yomi (音読み): がい (gai) ・Kun-yomi (訓読み): い (i) - This is the primary reading used when referring to the zodiac sign.

⚫︎亥年 Translation: The year of the Boar/Pig. ⚫︎十二支（じゅうにし） Translation: The twelve zodiac signs (亥 is one of them). ⚫︎亥の刻（いのこく） Translation: The hour of the Boar/Pig (9 PM to 11 PM).

The kanji 亥 is believed to be a pictograph. Some scholars propose it may originally depict the skeleton of a pig, or a pregnant sow, representing the idea of completion, fullness, and potential for new life, similar to a sow being full with offspring. Over time, the form of the character simplified to its current shape.