Late 8th century in the Roman Empire

This is the story where you are sent back into the past when the Roman Empire during the Isaurian dynasty was nearing its end and the Abbasid Caliphate was experiencing what is remembered as its golden age.

What will you do there? Living another normal life? Join the military to fight against the Bulgarians in the Balkans and the Muslims in the Middle East? Attempt to become the Basileus in one way or another? Or see to it if you can change history one way somehow?