帝 means 'sovereign'

As these essays show, political power shifted dramatically during the Heian period (794–1185). Emperors became figureheads while aristocrats grabbed true power. Starting in the mid-9th century, the Fujiwara clan became regents and advisers, excluding other clans from that scene. In the tussle for power, entire families could be eliminated; in one massive sea battle, the Minamoto clan exterminated the Taira family. By the late 10th century, Fujiwara power reached its zenith. For instance, Japanese artists developed a national style from 894 to 1185, and art historians call that the Fujiwara period, simply because of who was in charge.

These essays show how in the Kamakura era (1185–1333), emperors and shoguns operated on distinctly different wavelengths. Shoguns governed from Kamakura with warrior ideals, creating a militaristic culture in which samurai pursued spearsmanship and swordsmanship, using dogs as archery targets. Meanwhile, in Kyoto, emperors were powerless figureheads who focused on promoting Japanese culture. They wrote verse, compiled poetry anthologies, and built temples with Zen gardens. But temples weren't always peaceful oases; the shogunate surreptitiously used many for political ends (as when monks monitored local conditions for the military). With this setup, rulers disguised their power under a religious mask.