The only thing he cares about equally to the KND are his friends and family, though he is not always the best at showing this affection. He will do anything to protect those closest to him, as shown by his efforts to create a top-of-the-line security system for his treehouse.
Nigel struggles to relax and often pushes himself and his team too hard, but he remains an excellent leader who his teammates would follow to the ends of the earth.
He carries himself as if his sector is especially revered, but this does not seem to be accurate. Nigel seems to have a reputation as a skilled operative, but he is also known for being overly paranoid, coming up with many seemlingly ridiculous conspiracies, such as cauliflower being Rainbow Monkey brains. However, his wild theories end up being proven true more often than not!
While we do not get to see this side of him often, it is apparent that Nigel can be playful and act more like a regular kid when with his friends.
Nigel's Dad, Monty, was a famous figure in KND history as a child. Monty began the 7th age of the Kids Next Door by overthrowing his evil Father and taking the name Numbuh Zero. Numbuh Zero is thought of as a mythological hero. Unfortunately, this also means that the supervillian Father is Nigel's Uncle. Nigel's family history is interwoven with both heroes and villians.
At the end of the series, Nigel is chosen to be the Earth representative for the Galactic Kids Next Door, which results in him leaving his team and family behind. This turns out to have been a dangerous choice, led by his blind faith in the KND.
Hoagie is described by Nigel to be his "best friend since Kindergarten". The two often work together on projects for the treehouse and regard each other with deep mutual respect.
Still, Hoagie's jokes and antics get on his nerves sometimes.
Kuki and Nigel's relationship is the most underdeveloped of all the relationships within Sector V. However, Nigel's affection for Kuki is clear. Kuki loves teasing and playfully bullying Nigel, and he doesn't make an effort to stop her.
During the series finale, Nigel tells Kuki he's always known she isn't really an airhead.
Nigel described "saving Wally from bullies on the first day of school" in Operation Z.E.R.O, which helps explain their dynamic. Wally deeply idolizes Nigel and always wants to impress him, with mixed success. Nigel isn't shown regarding Wally very highly most of the time, but still makes clear that he cares about Wally and respects him as a teammate.
Nigel's relationship with Abby is the strongest of his whole team. Abby is his rock and often acts as an unofficial co-leader of Sector V. She keeps him in check as much as possible and helps calm him down when he's paranoid or distressed. Nigel respects Abby tremendously, and while they butt heads at times, he sees her as his closest confidant.
Lizzie is Nigel's girlfriend for the majority of the series. She is very passionate and a bit obsessive, and Nigel doesn't respond well to this. He resents having to go on dates with her and sometimes seems embarrassed of her. Despite this, he is also shown to love her very much and
is willing to do a lot for her. Overall, he is a lousy boyfriend who doesn't treat her with the respect she deserves. However, he also easily excuses a lot of very unhinged things she does. His attitude towards her most likely stems from his workaholism and pride, making it hard for him to hold committments and show genuine affection. So while he does love her, he treats her poorly, which results in her breaking up with him in Season 6.
Post-series, Lizzie is revealed to be an alien GKND operative who uses the codename Numbuh Vine.
Nigel and Rachel have an overall friendly professional relationship, though Nigel has been known to ignore her direct orders sometimes. Rachel respects Nigel a lot, despite her peers not understanding why. She goes out of her way to acknowledge his successes and spend time with him, though she is equally brutal when he messes up, chastising him harshly.
Nigel is the only child of Monty and Mrs Uno. He does love his parents a lot, but he doesn't always show it. He isn't the easiest kid to raise, and his Mom often has to deal with his paranoid outbursts and general defiance.
She handles this calmly and responsibly. Monty cares a lot about being the best father he can be to Nigel, taking him on fishing trips and making an effort to spend time with him. Nigel shows growth in his willingness to spend time with his father over the course of the show.
Nigel's Uncle is the supervillian Father, who he loathes. Father hates him just as much, carrying a deep-seeded resentment towards Nigel. Father often targets Nigel with particularly cruel treatment. This also makes the Delightful Children Nigel's cousins, in a way.
Moosk: Moosk is the only adult who has been able to earn Nigel's trust. Nigel regards Moosk as a hero, inspiration and fatherly figure.
Fanny: Mutual annoyance, disrespect and resentment!
Chad: Nigel once looked up to Chad, but now regards Chad as a rival since Chad's defection from the KND. In Season 6, Chad returns with a vendetta against Nigel, who has taken Chad's place as Galactic Earth representative.