Isshin Arima

Isshin Arima (有馬 一心 Arima Isshin) is the owner of the wealthy Arima corporation and grandfather of Teppei Arima who adopts him when Kanae Kobayashi (Teppei's mother) and Mr. Kobayashi (Teppei's father) were killed. Having learned his lesson with his daughter, Isshin allows Teppei to do as he wishes within broad guidelines rather than what Isshin wants him to do so that Teppei does not run away as his mother did. Isshin has an excellent memory despite his advanced age and, not having been a part of his childhood, wants to get to know Teppei better. 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 the automotive and metal industries.

Teppei Arima
Isshin's grandson. After his daughter (Teppei's mother) is killed in a traffic accident, he takes Teppei in. He enrolls him in a prestigious school to prepare Teppei as the successor to the Arima Corporation, as his daughter was his original successor.

Kanae Kobayashi
Isshin's daughter. It is believed that his relationship with his daughter was turbulent. Not wanting repeat his mistake that caused his daughter to run away, Isshin allowed Teppei to do as he wishes with broad guidelines.

Yū Fujikura
Isshin's adopted daughter and maid. When Yū was an orphan, Isshin took her under his wing. He groomed her into being his maid. From day that she was adopted, Yū was loyal to him.