On FANBOX, you can set a 500 JPY plan that allows supporters to view all your FANs only posts, then offer a 1000 JPY plan with no special perks for supporters who want to give you extra.
You can also create a donation-box-style plan where fans can offer donations if they want to support your work.
Of course, if you make promises to your supporters in your plan outline, you need to keep those promises. However, bear in mind that many fans who support you may not actually be thinking very deeply about the pricing of your plan.
The most important thing to consider when deciding on your plan is setting it at a level that allows you to grow as a creator while receiving support.If you make a plan for more than 500 JPY, try not to wear yourself out.