Don't Save Your Sister Casually

"I really can't do trigonometric functions!" Years ago, my sister was falsely accused and imprisoned, and only Dax believed the truth she told. Now, after investigating everything, Dax is determined to sneak into the prison and save his Onii-chan (hey), but unexpectedly discovers that this prison seems to be very abnormal - so which prison guard would test other people's functions? ! ——Thinking about it, Dax silently finished his sister's prison meal.