if you can put it in the Romanised Title field, it's rankable
if you can't, you can drop it or replace it with a similar character:
Ranking Criteria wrote:
Special unicode characters must be filtered to their nearest standard equivalent or removed from the romanised fields within a .osu file. ★ ☆ ⚝ ✪ and the likes are substituted to an asterisk (*). Other special characters are to be romanised or dropped on case-by-case basis.
if you can upload the map with the character in the diffname, it's rankable (invalid characters in a diffname give you an error message along the lines of "invalid character on line 10: version: asdf" when you try to upload the map)
