Haruki is a mod created for Doki Doki Literature club with intention of preventing Monika's influence on the other files, Almost like an antivirus. His main derivative is to "Save the girls" which he does so by overwriting the file deletions to be rather transfered to his own files; literally saving them while they still appear as gone from the game. However with each save he also gains a small virus/malware from Monika, who is aware and infecting him; hence why he gets more unwell as the game progresses. 
I cant believe i never uploaded this...