Gukki

Japanese: 虞喜 - ぐき

…Hipparchus determined that the lengths were 365 days, 5 hours, and 55 minutes (the true value was 48 minutes and 46 seconds) and 365 days, 6 hours, and 10 minutes (the true value was 9 minutes and 10 seconds), respectively. Yu Xi (281-356) of the Eastern Jin Dynasty in China independently discovered the retrograde motion of the winter solstice (in Chinese astronomy, the position of the winter solstice was considered more important than the vernal equinox), and pointed out the existence of age differences.
[Precession of the Earth]
The Earth is an oblate ellipsoid with a bulge at the equator, and the Earth's equatorial plane is tilted at an angle of about 23°.5 to the ecliptic (the plane of the Earth's orbit).

From [Chinese Astronomy]

…Furthermore, in the 6th century, Zhang Zixin of the Northern Qi Dynasty discovered the “central difference” of the sun’s motion. However, even before this, Yu Xi had discovered the “precession” during the Eastern Jin Dynasty in the first half of the 4th century. The “Koukyoku Calendar” by Liu Huan of the Sui Dynasty incorporated all of this knowledge and created a groundbreaking calendar system. …

*Some of the terminology explanations that mention "Yuki" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…ヒッパルコスはその長さをそれぞれ365日5時間55分(真値は48分46秒)および365日6時間10分(真値は9分10秒)とした。中国の東晋時代の虞喜（ぐき）(281‐356)は，独立に冬至点(中国の天文学では春分点より冬至点の位置を重要視した)の逆行を発見し，歳の差の存在を指摘した。
［地球の歳差運動］
　地球は，赤道部の膨らんだ扁平楕円体の形をしており，かつ地球の赤道面は黄道面(地球の軌道面)に対して約23゜.5傾いている。…