You only need to pay tuition fees to RU; it is not necessary to pay tuition fees to the ANU. Even while studying abroad, the payment, billing and deadlines will not change at all. Invoices for tuition fees will be sent to the 'Tuition Billing Address' and will not be sent overseas. If tuition fees are not paid by the due date, the student will under any cicumstance be "expelled" from the university and will not be able to continue their studies. To avoid such problems, it is important that you update your tuition billing address and your own address before your departure. Details will be explained at the Pre-Departure guidance session.
Furthermore, SSAF (Services & amenities fee) must be paid separately to the ANU, hence please follow the instruction by the ANU.
Regarding RU tuition payment
https://www.ritsumei.ac.jp/tuitionfees