Zelda: Ocarina of Time/Navi joins our team/Grammar

The imperative form using ～なさい

おきなさい！

You can form the "polite" imperative by taking off the ます off of a verb in the polite present, and add なさい.

食べなさい Eat 読みなさい Read おきなさい Get up

～なさい is used by superiors to their inferiors, like a parent to a child, or a teacher to a student. てください is used by inferiors to ask their superiors to do something, like a student to a teacher.

The word "polite" means this form is not the impolite imperative, like 　おきろ! Or 読め！, which is a lot stronger imperative.