This thesis focuses on the Colorful Realm of Living Beings, a set of thirty-three hanging scrolls by an Edo-period painter named Ito Jakuchu (1716--1800). The Colorful Realm was already considered a masterpiece during Jakuchu's lifetime. This thesis investigates the fundamental question of what made the Colorful Realm effective. The unifying concept is the "essence" of painting in eighteenth-century Kyoto. This study demonstrates that, as a painter immersed in intellectual circles and a devout Buddhist, Jakuchu integrated elements that tapped into ideas about the "essence" of painting in Buddhist, bird-and-flower, and literati painting traditions in the Colorful Realm to produce a set of paintings not simply beautiful, but also fully animated and perfectly appropriate for Buddhist rituals.