Maruko's kind but absent-minded grandfather. Naive and easily tricked, he keeps a pet turtle and loves watching TV with Maruko. When feeling distressed or nostalgic, he spontaneously retreats to a surreal inner world for a few seconds to improvise a sad yet comical haiku about his state of mind. His birthday is October 3, 1898, making him 76 in the series. The author has said that she used her own grandfather as the model for Tomozou, but that his personality is the opposite of Tomozou's.