This paper proposes a visualization tool, called Topic Tracer, to show topic transitions of not only a story existing in a document but also stories traversing over several documents. To visualize topic transition, first we have developed an analytical method to divide a document into parts. Then, we introduce a Word Colony to show topic terms in a whole or a part of document. It is a directed graph which shows the dependency relationships among terms occurrences in the target document. The Word Colony helps users to grasp the overview of a document. The concatenation of Word Colony gives plots of an existing story or crossing stories over several documents. This paper explains the concept and implementation of Topic Tracer using the minutes of the CUBESAT project, "Student-built Educational Pico-Satellite Design", in University of Tokyo.