Nobu is what most people who are up to date with modern slang would call a "cinnamon bun". One definitely wouldn't think he's a prince of an island unless he were to tell them, mainly because he doesn't portray himself as one. He's a very down to earth and go with the flow type of person - certainly not a strong leader like his mom or dad. But he is learning how, and he's come a long way from the bubbly and ditsy little kid who used to run around the castle, he's far more composed and poised nowadays - his manners are impeccable.
Deep down that little kid is still in Nobu, but since there are people in his families' kingdom that look up to him he has to portray the best him that he can. Sometimes he lets it slip, getting goofy here and there in front of his father's subjects. Although he doesn't seem like it, Nobu takes a lot of pride in not only himself but also his family for everything they've done.
Living on a seemingly uninhabited island in Japan called Kogajajima, was a royal pure-blood family with the last name of Hayashi. King Daichi and his wife Queen Aiko had long reigned the island and managed to keep the kingdom hidden to the muggle eye using the same type of veil used on Hogwarts, so all they saw was an abandoned island with a few half demolished buildings here and there. Their first born child was a female, Princess Mayu, and for the longest time they were happy with just one child. However the couple decided it would be best for their daughter to have a younger brother or sister who could grow up with them, and thus Aiko gave birth to a baby boy named Nobu two years after Mayu was born.
Nobu was a lively little guy, he was always running around the castle and causing mischief for the guards who would be assigned to look after him while Daichi and Aiko were doing their duties. Definitely not how a prince should be acting, but at his young age nobody questioned it and everyone found it cute. The cute and energetic prince was lively for the longest time, and his parents didn't expect him to ever stop his ways and take on the personality of an actual prince. Eventually his parents gave up on changing his personality to a poised one, figuring time would be the best way method. And overtime Nobu did seem to settle down, he became more respectful and also quieter. Taking on true characteristics of a prince.
At the age of eight, Nobu had his first magical encounter. He was eating dinner in the dining room with Daichi, Aiko, and Mayu when he went to grab his glass of water but instead it shattered when he just looked at it. Nobu was confused as to what had happened but Diachi and Aiko, being pure-blood and having experienced it themselves, knew it was just his magic kicking in. After that experience, Aiko taught Nobu a little bit about magic up until he was accepted to attend Mahoutokoro after his eleventh birthday.
While attending Mahoutokoro, Nobu got into quidditch after a friend had convinced him to try out for the team. He was against it at first, but after trying out during his first year he grew to love it and eventually made the team as a chaser. Nobu played as the chaser all throughout his seven years and later he returned him to his kingdom in Kogajajima.