The line in question is found in act three, scene one of William Shakespeare's Twelfth Night. It is spoken by Maria during a conversation with Sir Toby Belch about Sir Andrew Aguecheek.
The figure of speech (or poetic device/ literary device) which appears in the line in question is alliteration. Alliteration is the repetition of a consonant sound within a line of poetry. Given that the question is so specific, and only offers a fragment of the poetic line, this is the most apparent figure of speech. In this example of alliteration, "he had indeed, almost natural," the "h" sound in "he" and "had" repeat.
One other figure of speech is assonance. Assonance is the repetition of a vowel sound within a line of poetry. In the line in question, the "a" sound in "had" and "natural" repeat.