Plain form as imperative

Question

Is the plain form ever used to give a command? What does "sugu ni tatsu" mean?

Answer 1

Yes, 終止形 can be used as a command like in this manga. Translation: "Then stand up right away!"

It sounds like a parent or a school teacher ordering their kids to do something right away. It's weaker/friendlier than 立て but stronger than 立ってください.

Such use of 終止形 is not usually heard in military organizations, so I feel the person on the right is being rather friendly rather than dignified as a supervisor.

Negative form is also possible. Example: 「(教室で先生が)そこ、喋らない！」「ごちゃごちゃ反論しない！」