Jaa Mata ne Kanzenban

Yuuko is an average 5th grader from the late 1960s whose friend gives her a brown tabby kitten. She names her Tiger. Yuuko and Tiger grow up together, although Tiger is, of course, much quicker to mature. From 1967 to 1970, Yuuko goes through a formative four years from childhood to young adulthood where she learns about time and space travel, sports, and... where babies come from! Just wait till she tells Tiger about this! What Yuuko doesn't know, however, is that Tiger understands everything she is saying and looks after her more than she will ever realize... (Source: Manga Planet) Note: Includes three extra chapters.