When first mentioned back in February, Nintendo was said to be working on Oni Tore, or "Demon Training"—a quiz that tested the ability to work on problems from memory. During the Nintendo Direct showcase on Friday, the company offered a look at one of its minigames in action, Oni Keisan, or "Demon Calculation."
In Oni Keisan, a math problem appears, then disappears, and you have to solve that problem as another math problem appears. That problem disappears as you are solving it, and is replaced by another problem, and so on.
The game is meant to help your "working memory" by requiring you to solve the new problem in your mind, then answering the old question.
Oni Tore will have other "working memory" challenges, too.