Comes from "real" and "literally." Invented to compensate for the dramatic over- and mis-usage of the word "literally." What people now say as literal will usually not actually be literal, so the word "reliteral," or "reliterally," was invented to actually mean literally, and present no confusion as to whether the statement is actually literal or not.
"I swear, I literally have like four million cats." (misuse of "literally")
"I reliterally have seven cats. I can name them if you want me to." (correct!)
"Oh my god, I will like, literally have ADD if you don't stop talking." (misuse)
"I reliterally have ADD, I just found out from the doctor today." (correct!)