As we get closer to the Monster Hunter 20th anniversary celebrations, Capcom has announced the "end of collab DLC" content for Monster Hunter Rise.
This means you need to download this free content before 21st January 2024 to "keep using it as normal". After this date, it will no longer be available. This includes some Sonic the Hedgehog, USJ and Sengan-en collab content.
You can see the exact collab content that will be impacted by this in the table below:
"Monster Hunter: Heads up, hunters! The following #MHRise collaboration content will no longer be available to download from January 21, 2024 if you do not already have it. Please download this free content before then to keep using it as normal. You won't be able to redownload it."
Capcom hasn't provided a reason as to why this content is being removed, but there's a good chance it's linked to licensing. So, if you want this content, download it while you still can.