Happy set "Demon Slayer" original sticker
(The image is quoted from the official website)

The "Happy Set" sold at each McDonald's store comes with an original "Demon Slayer" sticker. Limited quantity. Released on March 5th.

Comes with a sticker set and an extra toy. It's random, so I don't know which one you will get. Also, the bonus toys are not "Demon Slayer". There are 5 types in the lineup.

(C) Koyoharu Gotouge / Shueisha / Aniplex / ufotable