On Ja

Coming from the legend Ja Morant, another way of saying "On God." If you say something is "On Ja" you're deadass and not messin' around. "On Ja" can also be used to agree with someone.

Ja Morant is the only 12 I F*ck wit, that's on Ja.

Person #1: "Polo G is the best to ever do it, no kizzy"
Person #2: "On Ja bro"