In his teenage years, Osanai had the standard bleached delinquent pompadour. He had narrow and menacing eyes and sported a smirk as his standard expression. His prominent feature is a diagonal scar across his forehead. He wore a standard Moebius uniform.
In the present, Osanai's hair goes back to its natural black color. His eyes become more mellow and he is missing some teeth. He puts on weight and develops a hunchback. Due to his job as a construction worker, he wears the uniform of his profession.
As a teenager, Osanai is brusque and violent. He looks down on other delinquents not in his gang and is highly confident in his fighting abilities. He is also quite dim-witted, easily getting manipulated by Tetta Kisaki to do his bidding.
After suffering from life as an adult, Osanai has become a shell of his former self. He turns into a meek and mild-mannered man who apologizes for anything he does and easily gets startled.
Hearing that Tokyo Manji Gang is looking for a fight, Nobutaka finds Mikey and few other members and mocks them for being younger. Pah-chin gets angry, but Nobutaka easily beats him and then calls his gang who surround the Toman members.
Nobutaka sees Takemichi looking at him and feels he is looking down on him and starts beating him. Pah-chin then stops him and decides to take him on. Nobutaka showcases boxing skills and easily beats and breaks Pah-chin's nose. Manjiro then steps in and Nobutaka wonders if he wants to fight him too, but in that instant, Manjiro kicks Nobutaka in the head and knocks him out. Few moments later, Nobutaka awakens and grabs a broken bottle and attempts to attack Manjiro and Ken Ryuguji, but Ken easily neutralizes him. While Ken holds him, he tells him that he lost due to losing his delinquent way and raped a woman and assaulted the family of someone. Ken then announces that Moebius will be under Tokyo Manji Gang, police sirens wail and everyone starts to run. However, while Ken still holds Nobutaka, Pah-chin comes from behind and stabs him in the back. While the rest leaves, Pah-chin stays to surrender himself to the police.
In the present, with Ken Ryuguji's death, Nobutaka's life has turned bad and he works as a construction worker. After being late for work and scolded again, Takemichi Hanagaki and Naoto Tachibana find him and wish to talk with him. After explaining they are there to talk about Toman's fight 12 years ago, Nobutaka initially refuses to talk, but denies Naoto's accusations that he ordered Ken's death. Shaken, Nobutaka reveals that all was planned and he used as the incident led to Toman's internal conflict. Before leaving, he reveals that he wished Ken to not have died as that ruined his life.
Osanai, in his heyday, was a very competent fighter. He led Moebius through sheer might and fear alone, hinting that he was the strongest in the gang at the time. He was able to easily defeat Pah-chin, whose skills were even lauded by Draken. Although strong, he still fell to Mikey in a single blow and was effortlessly subdued by Draken.
- The name Nobutaka means "trust, believe" (信) (nobu) and "tall, high" (高) (taka).
- Nobutaka's surname Osanai means "long, chief, boss" (長) (osa) and "inside, within" (内) (nai).
- According to the official character book:
- His image color is wine red.
- He likes John Travolta.
- He dislikes twisted guy.
- His special skill is boxing.
- The person he respects or admire is Joichiro Tatsuyoshi.
- His dream is to make a fortune by running a club.
- His heroic story (or failure story): He won't lose to the delinquents of his peer.
- His favorite spot is Moebius' meeting place.