The first-month fee goes for the “monthly basic charges” of data transmission on the month you start the contract. The monthly basic fee includes mandatory charges for data transmission and other underlying fees (SMS Basic fee, Voice Call Basic fee).
Example:
 |  |  | Monthly basic fee (tax included) | |
| DATA 6GB (Data only option) | 3,058 yen | 165 yen | (not available) | 3,223 yen |
| DATA 6GB (050 Voice Call plan) | 3,058 yen | 165 yen | 330 yen | 3,553 yen |
The monthly basic fee is the fixed amount that charges you each month for activating sim card service. Besides, you will have to pay for your usage fee if any.