Kogetsu Zenzai (1667âÂÂ1751) was a Japanese Rinzai Zen monk who emulated à Âbaku-teachings into Japanese Rinzai Zen. His teacher Kengan Zen'etsu (1618âÂÂ1696) had trained under Chinese à Âbaku-monks, and Kogetsu Zenzai was one of the principal persons in assimilating their teachings. In contrast, Hakuin Ekaku (1686âÂÂ1768) opposed their influence, yet also stressed the need for rigorous practice. A number of influential students of Kogetsu Zenzai eventually also studied with Hakuin, creating the koan-system presently used within Japanese Rinzai-Zen.