Saying you can't learn ninja because of storyline Is like saying all new player get to see mor dhona progress. They don't certain things in earzea are constantly changing. According to lore with Rev toll where it's at yugiri and her people are easy made present, with the explanation of how they got there in the storyline. Rogue, as than cred shows us. Already exist in the game, ano he picks up ninja super fast, so rwally they just need a than rid type nic to travel to yugioh land and traon, then return. Yugioh doesn't even have to be part of ninjas story.