The mod above me is inactive and doesn't answer messages. What should I do?

I became a moderator of r/HikarugaShinaNatsu about a year ago, after I submitted a reddit request. The inactive mod magically reappeared and added me as a mod instead of letting go of the subreddit. Fast forward a year, and this person is still completely inactive and doesn't even seem to use Reddit anymore. I'd like to have them removed if possible, since they don't contribute anything and don't answer any of my attempts to communicate with them. Is there a way to go about doing this?