Like many countries, Japan uses a 12-month calendar. The names are very simple. January is literally “Month one” 一月, February is “Month two” 二月, etc.
However, before the Meiji Restoration (mid-1800s) it was common to use an older 12-month system. These months’ names referenced the weather and the seasons (similar to the French Revolutionary calendar).
April is 卯月. Japanese learners will recognise the kanji 月 as “moon” or “month”. The first kanji is less common. It is most often used to represent the Sign of the Rabbit in East Asian Horoscopes, and the Year of the Rabbit uses this sign too.
So what is the connection between April and rabbits? Perhaps nothing. It is thought that 卯 was originally 植, which has the same sound. 植 is the kanji for “planting”. This refers to rice planning, which is carried out every spring throughout Japan.