1. First, You decide the accounting method on dealing with a consumption tax.
There are two methods, one is to account all prices with a consumption tax included, and the other method is to account all prices without a consumption tax.
Most self-employer business persons use the accounting method including a consumption tax. This is because that does not need to master the complicated rules of Japan consumption tax to record your transactions.
2. It depends on your method.
If you use the the accounting method including a consumption tax, you have to use the prices including a consumption tax in order to determine whether it could deduct or not. On the other hand, if you use excluding consumption tax accounting method, you have to use the prices without a consumption tax.
Therefore, when you use excluding consumption tax accounting method, you could deduct more purchases generally. This could work better for your personal income tax.
3. You could use both accounting methods on some payments, only when you use excluding consumption tax accounting method on your revenue.
This is rather complicated to understand why this is allowed and what this is useful for. Accordingly please contact and ask me, if you are interested in this accounting.