I'm sure I'm going to be stating the obvious quite a bit, but meh.
In anime, or any visual art, the world shows itself. You cannot monologue and tell the motivation, you need to show through visual action. Subtleties can be places all over the place to set the tone. And the viewer is pretty much a 'fly on the wall'. You need to put enough of the right kinds of action to keep your core audience happy, and to attract newbies to the stands. You cannot tell what's going on, you need to show it.
Sounds like how people profess they write, doesn't it?
Except, it isn't. When you draw, you see the same thing someone else sees. Sure, your focus might be somewhere else, but you're getting in the same image.
When writing, all you have is words. With these words, you must sculpt the world in which the magic happens. You cannot subtly hint at something with a 'screenshot' that hides the clues. You need to show something with words and keep the reader guessing the hard way.
More importantly, writers have tools anime and visual artists never get: Emotions, Feelings, thoughts.
Instead of showing anger in facial expression, a writer describes it. A downward curl in the lip, an upwards tug in the cheek. Balled fists, a razor sharp glare. A burning fury within our beloved hero, one which is struggled against to not make things worse. Perhaps a queasy feeling in her stomach, as she sits next to the boy she's secretly in love with.
And perhaps most importantly, the difference in word choice. It isn't as pronounced in any visual art, because words are less than 20% of communication. Now, words are 100%, it's literally all you have.
She shuffled her feet, drudged through the class, and slumped into her seat. "G'mornin'," she grumbles, rubbing the back of her hand against her eye.
She bounced through the crowd, making a beeline for her seat. She's wearing the hugest grin ever! Her eyes dart to and fro, taking in rays of light as they bounce off the happy people around her. "Good morning, everyone!"
She hums a catchy tune, a song she heard on the radio that just got stuck. The buzzing crowd she finds herself in drowns it out, but she doesn't mind. She passes her classmates, making her way to her seat, right beside Mina. "Someone's in a good mood," Mina grumbles, glaring at her.
The words used set the tone. Descriptive language colours the picture, and can make or break your scene.
Hope this helps ^_^