late last year and now, people in japan thinks that emperors and their DNAs probably are south east asian, and they migrated to japan through the land bridge during ice age passing through okinawa, and came from taiwan, filippine, vietnam, malaysia, thailand, and indonesia. many similarities found with indonesian, malaysian, vietnamese.
I know many japanese scholars and people are supporting the contributions from south east asia.
Linguistic, malaysian, bahasa, indian tamil and japanese may be in common origin with the way it uses the plural and subject. Japanese Y haplogroup O2b1 and D2 are also south east asian, and indonesian/vietnamese both share this haplogroup, which Malaysian should also have with more DNA tests on tribes.
I hope topic is acknowledged better outside japan, and more scholarly researches will in future.
Origin of Imperial House of Japan
another article is helps me.
Imperial family descended from Jomon/Ainu of Japan
The History of Japanese Houses
In ancient Japan, there were essentially two different types of houses. The first was what is known as a pit-dwelling house, in which columns are inserted into a big hole dug in the ground and then surrounded by grass. The second was built with the floor raised above the ground. The style of house with an elevated floor is said to have come to Japan from Southeast Asia, and this type of building was apparently used to store grain and other foods so that they wouldn't spoil from heat and humidity.