Koichi Takeuchi was born in Kyoto in 1941. Growing up in a Yuzen dyeing family, he was surrounded by patterns and colors that nurtured his sensitivity to beauty from an early age. After studying Nihonga in high school, he worked in textile design, but at the age of 25 he chose to dedicate himself fully to painting. He entered the Shinchōsha school and studied under the celebrated animal painter Kayō Yamaguchi.

His sharp observation and distinctive brushwork soon attracted attention. By the late 1970s he had gained recognition at major exhibitions such as the Yamatane Museum Prize and the Nitten, marking his place as a rising artist. Through the 1980s and 1990s, he joined colleagues in forming study groups and collectives, pursuing new possibilities in Nihonga.

From the 2000s, Takeuchi also served as a professor at Kyoto City University of Arts, fostering the next generation while continuing his own creative journey. He produced large-scale works such as the fusuma paintings at Hōshun-in in Daitoku-ji Temple, affirming his place in both traditional and contemporary contexts.

The animals he painted—foxes, gibbons, horses, and birds—go beyond naturalistic study. Each line of fur drawn with ink conveys both softness and tension, as though breathing life into the image. His works evoke affection and awe at once, blending classical techniques with a modern sensibility and setting a new standard for the depiction of animals in Nihonga.