Rintarou has the characteristics of a lanky young man, with a square jaw and bony cheeks. He has his short black hair swept back and has brown irises, with a small amount of stubble on his chin. Rintarou also wears a lab coat, which he wears over a simple shirt and slacks.

Rintarou is a melodramatic, eccentric individual. He is a self-proclaimed mad scientist, who likes to assume the nickname "Kyouma Hououin" (鳳凰院凶省Elt;i>Hōōin Kyōma),which was given to him by Kurisu, and often uses this to introduce himself to others. For the most part, people do not seem to care and instead address him by his actual name or by 'Okarin' (his nickname), much to his chagrin.

He also likes to pose as an agent working against a certain "Organization" which he thinks is always after him, as he believes this kind of image gives him a cool and mysterious aura, though this seems to disappear as the story progresses, with SERN likely replacing the "Organization's" villainous image.

He usually gives off the impression of being delusional and paranoid, engaging in strange mannerisms such as talking to himself on the phone and engaging in fits of maniacal laughter often, this is in fact a façade he wears in order to make life interesting for his dear childhood friend Mayuri. Initially, he is portrayed as being rather arrogant, however, it is later suggested that this is due to Rintarou's eccentricities and social awkwardness.

Despite the aforementioned traits, he is actually a kind and caring individual. This is particularly evident towards the end of the anime and the visual novel, where he casts aside his peculiar façade, to save his friends from the seemingly unavoidable fate of the Alpha worldline.

He and Itaru are both students of Tokyo Electronics University, and have been friends for roughly three years, according to his words, although Itaru claims that their friendship was only about a year old.
Rintarou runs the "Future Gadget Laboratory", a small research institution situated above a CRT store. It is an area where he and his fellow Lab Members create "Future Gadgets for the betterment of mankind".

Rintarou has always been close friends with the second Lab Member and co-founder of the "Future Gadget Lab", his childhood friend Mayuri, who he made a vow to protect when they were young.

Rintarou lives an average life with his small group of friends until he creates the Phone Microwave with Itaru.