Hmm. Had to do a bit of digging on Japheth as I'm not well versed at all on him.

From this link - https://www.compellingtruth.org/Japheth-in-the-Bible.html:

Through Japheth's story, we learn of humans' need for rescue from the power and consequences of sin. God provided a way for Japheth to escape the flood by entering the ark. The flood came and went as God's wrath destroyed all who were not inside the ark. While the ark saved those inside from the raging waters, it did not save them from sin. Only faith in Jesus' work on the cross and His resurrection can rescue us from the power of sin in our lives (Romans 8:2). Like Japheth and Shem covered their father's nakedness with a cloak, Jesus' righteousness can cover our lack of holiness (Philippians 3:9). Praise God that He provides this way of salvation for humanity in need (Romans 1:16)!