Fans predicted that Judal and Alibaba were stuck in the upper grounds of Alma Torran. Come chapter 275, it's proven true.
Before chapter 276, there are fans who predicted that Sinbad would be the villain given the idea that he had half-fallen to depravity. And 276 just confirms it and had him connected to David.
Fans who believed in the He's Just Hiding idea back at the YMMV for Arba/Gyokuen suspected that Arba found a vessel through Hakuei and gave birth to the Arba possessed Hakuei idea. Some of the fans who didn't believe it thought of it as a joke, but come 282, it's been proven true.
In early designs, Alibaba was supposed to be a gladiator, with a quieter and inexpressive behaviour. Ohtaka discarded the idea because, according to her, she's better creating more expressive characters. This ideas, however, got her into creating Masrur.
Ohtaka once said that Spartos was originally supposed to be a woman.
Hakuryuu was supposed to be the older brother and Hakuei the younger sister, Ohtaka mentions that the story would've been quite different.
Ohtaka also originally thought of making Drakon and the similarly draconic Shou En (one of Kouen's household members) brothers.
Marga originally was going to be older and Titus' love interest.
Word of God wanted to draw Yunan as a middle-aged man, but she was requested to draw him as a delicate man. That's why she tried to draw him with the feel of a tired widower.
Myron was originally planned to be male until it was scrapped off because her early designs make her look like a prettier looking Ka Koubun.