Someone knows where I can Buy Sekiro for a good price?

It's only ever been -50% https://steamdb.info/app/814380/

It's Activision, they don't generate keys for some games, this being one of them. Unless by some miracle it's in a Humble Bundle a decade or two from now.

IsThereAnyDeal is useful for something like this. There's currently no sale, but it goes on sale for 50% off every few months, so if you're patient you can add it to your wishlist and wait, and at least get half off.

With a simple comparison of USD to R$ as an indicator of financial purchasing power, people from japan should have much much more difficulty in buying anything. 1 USD = 144 JPY.
You should change all your R$ into JPY and live there. :)