There's really no need for the tag to be "index_(to_aru_majutsu_no_index)", as this is usually used when there are multiple characters with the same name. I'm going to suggest an alias to simply "index"
Yeah, I was thinking the same thing too. I really don't think "index" is necessary as a general tag. Best to leave it for the character in my opinion so we can avoid an unnecessarily long tag.
I originally created the long tag name because index was already in use in posts such as post #172251. Now that the character Index is getting more attention I think it's fair to shorten it considering how little use the old index tag was getting.
Roastbeefy has cleaned up the old tag by replacing it with table_of_contents where needed, so approving the alias shouldn't bring up any issues.