some fix

You should use [esc_textarea()](http://codex.wordpress.org/Function_Reference/esc_textarea) than esc_html() in the textarea.

It will be easier to customise via another plugin like below.

```
add_action('plugins_loaded', 'my_plugins_loaded', 11);

function my_plugins_loaded() {
    remove_action('edit_category_form_fields', array($expand_category_sakai, 'extra_category_fields'));
    add_action('edit_category_form_fields', 'new_extra_category_fields');
}

function new_extra_category_fields() {
    echo '<p>Hello!</p>';
}
```