User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-32599925-20170722182822/@comment-4802891-20170725152408

I think he is Vespasian, Emperor of Rome from 69 AD to 79 AD. He was a prominent figure during the Jewish Revolt (his dialogue about David gives a hint), propaganda was a big part of his 10 years reign and he is the one requesting the building of the ampitheatre known as the Roman Colosseum.

I think Hikaru's Flavius is refering to Vespasian as well (both Titus and him had Titus, Flavius, Caesar, Vespasianus and Augustus in their name so... yeah, way to be simple guys lol)