Hi. Kaja, Kayo and kaji are Let's go. but There is an honorific words in korea. Kaja is for word between friend or younger than you. Kayo is for word to older than you or stranger. Kaji is for word between friend or younger than you. That's similar like Annyoung or Annyounghaseyo. Annyoung is Hi between friend. Annyounghaseyou is Hi between stranger or older and you (an honorific) I hope it will be support to you. bye.