From JShoujo Scans：

Takeshi is an 18-year-old boy who, due to his weak heart, had to repeat a year of school. He is heartbroken when he finds out the cat he had been raising for four years named Mika disappears. But the very next day, he meets a girl with the very same name! Her suicidal tendencies and eccentric nature though are nothing like his beloved pet. Where did his cat go? And why can't he stop thinking about this girl he just met?