Kimi to Boku no Uta World's End

Kimi to Boku no Uta World's End (君と僕の歌 world’s end) is a light novel series by Tsumugu Hashimoto with illustrations by Otohiko Takano.

Plot
In a world where everything was lost, our paths crossed. An unidentified epidemic exterminated humans in half a year. Hazufumi, a teenager who miraculously survived, lived lonely in this desolate world. He rejected to attain important things because he knew the pain when losing them... He happened to cross by a girl. A weird girl being followed by a hundred cats.And meeting with her changed Hazufumi's heart.