Final answer:
The correct word to use in the blank is 'defends'.
Step-by-step explanation:
The correct word to use in the blank is defends.
In the sentence, the subject is 'my brother' and the verb should agree with the subject in number. Since 'my brother' refers to a single person, the singular form of the verb 'defends' should be used. For example, 'My brother defends our country from enemies.'