Chiteki de Cool na Kouhai Bijo, Ore no Kai Neko ni Naru.

I was in bed with a cold, when a beautiful girl with cat ears appeared by my side. She claimed that she was my pet cat, transformed…!? The cat usually acts cool, but the cat-girl is all dere-dere. A love story with a mysterious beauty—. The popular YouTube video-manga with over 2.5 million views serialized on the Web!
(Source: Comic Newtype, translated)