Welcome to Quotev!
"Claiming" is typically something users on this site do. If they happen to like another individual, they'll "claim" them, meaning they will post an RA about it and tell you so, usually adding "HISS MOTHERFUCKING HISS" and will literally kill you if you ever treat them badly or touch them. This is obviously called a "Yandere", but in the world of Quotev it's simply another user doing what users do.
I advise you to not dare mess with another's claimed one, or there will my consequences, my friend. :)
Watch your back if you dare do so.