How do I remove an Emoji Reaction?

I was looking at this post and trying to figure out wat that Reaction Emoji was (a human with a mask and cape? wat does that mean?) but I clicked on it by mistake. Now if I mouse-over it, it shows my name as someone who reacted that way.

Then I tried to "unclick" it but found no way to do so. (using default web interface).

So it looks like I reacted with that emoji, even tho I didn't intend to and I don even know what that emoji means. Is there some way to remove my name from the list of people who clicked it? Thanks.