Azuki bean
Azuki beans have been grown since the Yayoi  period.  The first time the word "Azuki" was used was in the book "Koziki".  Old Japanese said "Aka" for red.  And Azuki beans were called "zuki" because  Azuki beans get soft when they are boiled.  "Aka" plus "zuki" is "Azuki" and this is the origin of Azuki bean's name.  Another Azuki beans has many origins.