The owner of the wealthy Arima corporation and grandfather of Teppei. He takes on Teppei when his parents were killed. He wants Teppei to do as the boy wishes rather than what Isshin wants so that Teppei doesn't run away like his mother did. Isshin has an excellent memory despite his advanced age and only wants to get to know Teppei. He was an entrepreneur during World War II and made his fortune in the aftermath of the war. His company extends into many areas including automotive and metal industries.