Why do you think the Mayans created a codex?

The Maya developed their huun-paper around the 5th century, which is roughly the same time that the codex became predominant over the scroll in the Roman world. Maya paper was more durable and a better writing surface than papyrus.This codex deals primarily with astronomy: days, calendars, good days for rituals, planting, prophecies, etc

cultural/diplomatic relations. most medieval japanese   culture has chinese origins. writing, architecture etc.