So, I just found out that you cannot get Aptitude on any Gen 1 character (except Mozu) in Fire Emblem Fates without hacking your game.
But I have Aptitude on my Leo and Hana, and I didn't hack. I bought it off another castle thinking that you could get it in the game.
And now the skills are stuck on my characters. But I've unequipped the skills.
Although this doesn't affect your save data any way, I thought I'd just warn other Fates players so that the hacked Aptitude skill doesn't spread.
You also can't get skills like Hoshidan unity and Nohrian Trust on any Gen 1 character.

ESTÁS LEYENDO
Blizzard's Random Update Book!
RandomIt's in the title :). And thanks to @Gamergirl80 for making the cover!