The notification of move and notification of arrival both have their specific purpose:
You must submit an official notification of move to the Population Register Centre within a week of your move. You can do this online on the Population Register Centre website.
The notification of arrival can almost always be filled in on the website of your maintenance company. It helps the maintenance company register you and any others moving in with you as residents of the building. This way they can place your name on your door and the list of names at the entrance to your building.
Remember that the notification of arrival does not replace the statutory notification of move, which you have to take care of separately.
If you need help in filling in the notifications, contact SATO Customer Service. We will be happy to help you.