Final answer:
The instruments added to enhance the mood of the most agitated theme in Romeo and Juliet are the shamisen, a traditional Japanese string instrument.
Step-by-step explanation:
The instruments added to enhance the mood of the most agitated theme in Romeo and Juliet are the shamisen, a traditional Japanese string instrument. The shamisen plays music in the background to create a specific atmosphere and evoke emotions in the audience. In this particular scene, the use of the shamisen with its unique sound and melodic style helps to intensify the agitation and tension experienced by the characters.