Which passport to study as dual citizen

Hi, I am 20 yrs old and i am half japanese. I have lived in australia my whole life, and i have an australian passport and japanese passport.

I have been accepted into studying an exchange program to japan. But I have dual nationality so I dont know which passport i should use to get into japan. It says that I cant get a student visa because i am a japanese national so i have to enter japan using my japanese passport. Is there any limitations to this? Would i be excluded for anything?

i am thinking to renew only my Australia passport and enter Japan, even if my japanese passport is expired would i be able to get in?

However both of my passports have expired. Should i only renew my Australian passport and use that to get into Japan, and then renew my japanese passport after i come back from exchange?

Renew both.

Use Japanese passport to gain visa free entry.

Use Aussie passport to get discounts that normally only tourists get.

I would renew both too.

Otherwise, you�fd have to go through the student visa application procedure to enter Japan (on your Australian passport).

it is better that you should make your passport not being expired, especially a foreign one. it needs to take laborious paperwork to get a new one.