Kusuo and Kusuke have always been fighting with each other in terms of their abilities and intelligence. However, being a psi user, Kusuo always win towards the genius Kusuke. Kusuo always thought that his brother hated him about it but Kusuke corrected him that he didn't hate him at all and it was the opposite as Kusuke was obsessed of Kusuo. Kusuke is both sadistic and masochistic towards Kusuo because even though he knew he'd lost, Kusuke will still challenge Kusuo.
Kuniharu is Kusuke's father. While he appears to barely acknowledge him, Kusuke shows that he is merely joking with him as he really loves his father as in his childhood he'd show off his inventions or acts to him.
Kusuke cares deeply for his mom.
Like his brother, he is immune to Teruhashi's beauty. He also doesn't think she and Kusuo are a good match.