because the theme is iced i got an idea to make cirno from touhou as main character is it okay?
The jam page states: Credit any assets you use, verify you have the proper license to use them
This means if there is a character such as an OC that you own the rights to and/or your create something of your own intellectual property then that is allowed. Characters that you have not made or do not have permission to redistribute/utilize are not allowed.
I hope this helps clarify. Let me know!