| 羽瀬川 隼人|
|Novel Debut||Volume 4|
|Manga Debut||Volume 7 Chapter 35|
Hayato has yet to make an appearance in the anime, but judging from the words of Kodaka and Tenma Kashiwazaki, he looks almost identical to Kodaka in terms of overall physique, especially facial features. Kodaka having obviously inherited his dark skin and eyes from him. The only visual difference is Hayato's black hair.
While Hayato and his son's looks are similar, their personalities are quite the opposite. He seems to be a passionate scholar who's prepared to sacrifice time with his family for his work. He is however, aware of this and always tries to somehow compensate for his lack of interaction with them, and is overall a responsible father (working hard to purchase a house that would fit his then pregnant (with Kodaka) wife's tastes. On the other hand, he seems to have a rather easy-going personality, being consumed by his interests, teasing Kodaka and is lacking manners (to Tenma's complaints). In contrast to the shy Tenma, Hayato seems to be quite straight-forward and even brash. He seems to be protective of his daughter, Kobato, as seen during his phone call with Kodaka.
Not much is known about his academic performance, but the fact that he spent his school days with Tenma, who descended from a rich family, is very intelligent and attended St. Chronica, indicates Hayato's excellent intellectual abilities, as he seems to be born in a middle class family (Hayato worked hard to achieve current wealth), and couldn't possibly attend it being a mediocre student without financial help.
Another more reliable indicator is the fact that he is quite famous in his field and often (from memories of Kodaka) has been visited by famed and much older scholars in his days in Japan.
According to Tenma, Hayato (along with his wife) was a good drinker, being able to withstand exceedingly large amounts of alcohol.