Koishimaru Tensan (テンサンコイシマル) is the protagonist of Medarot 5. He moves to Susutake Village with his family and enrols in the local school as a transfer student. Koishimaru is spunky and energetic, sometimes overly so, which makes some of his peers think he is strange, but he is easy to get along with and quickly makes friends. He cares about others and will go out of his way to defend others and help people.