If you are getting notifications from MainCharacterSearch, then your Mac is infected with adware. MainCharacterSearch is adware for Mac.
MainCharacterSearch changes setting in your Mac. First, MainCharacterSearch installs a browser extension in your browser. Then, after MainCharacterSearch hijacks your browser, it modifies settings in the browser. For example, it changes the default home page, modifies search results, and displays unwanted pop-ups in your browser.