There should be something that it makes the belt appear on the tori in a fight or something, When it's custom belt you can make textures or buy textures for it and stuff

You can always create your own textures for belts, but maybe after you rank up (belt rank) you get an option to buy that belt color

its an interesting idea,but i would only support if the belt item
was not customizable,it should show your belt color only and nothing else.

I like the idea too, but if I remember correctly they don't want to implement belts because in their opinion it looks ugly. Who knows, perhaps in the future it might be implemented ! (I'm always up for new cosmetics.)

You mean something like this?
if so, supported.
Would look awesome!
But how would you show differences between a 9th and a 10th Dan? Writing numbers on it?

How would you show from 1st Dan up?
I would say make it a buyable item like the custom belt.
Do an add on with the already custom belt in the shop which goes for more adding the belt texture. But having to earn it?
Thats my two cents

Like this :
https://imgur.com/a/49qL3

And I think for the custom belt, the player can choice the texture of his belt

This is honestly not bad idea at all. If there was for example some kind of option that allows you to enable or disable you belt from showing up, it would be cool.

also this:

you don't buy custom belt,you buy an item that allows you to change
your belt name after you get custom belt.

Now,about how the item could look for black belt-10th dan,if you guys
look at the images in the achievements,you will notice that on the right
each belt has a white thingy,no white thingy for black belt,10 white
thingys for 10th dan.

I guess the hard part in the item would be to make each one
distinguishable.

I know about the custom belts and all that.

I get that with the achievements, I went and looked now. Very hard to see unless you click on the achievement itself.

I suppose that would be true.