|Arima Isshin有馬 一心|
|Hair||Goatee, Moustache, White|
|Visual novels||Side character - Princess Lover!|
|Voiced by||Hiruma Kyounosuke|
The owner of the wealthy Arima corporation and grandfather of Teppei. He adopts Teppei when his daughter (Teppei's mother) and son-in-law 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 like his mother did.