The Kumo ninja would likely be angry at first. They'd feel that Naruto, as a symbol of hope in the shinobi world, should have noticed their problems. But some of them might also be hopeful that Naruto's arrival would finally change things for the better. As for Naruto himself, he'd probably be shocked to realize how much he'd overlooked Kumo and would feel a sense of guilt.
Kurama might become angry at first. He's a powerful being and being neglected would likely wound his pride. He could start causing some minor disruptions inside Naruto, like making it harder for Naruto to access his chakra.
The Z - fighters like Krillin and Yamcha would be curious about Naruto. Krillin might try to befriend him quickly, while Yamcha might be a bit jealous if Naruto starts getting a lot of attention. In the Naruto world, characters like Sakura and Sasuke might not even notice Naruto's disappearance at first if he has been neglected. But later, they might realize the importance of Naruto when things start to go wrong in their world without him. And in the Dragon Ball universe, Piccolo would be very watchful of Naruto, trying to figure out his motives and if he poses any threat to the safety of the planet.
She might feel guilty. Since they are siblings, she could be aware of Naruto's neglect and try to make it up to him in small ways, like sharing her food or secretly leaving him little gifts.
He might become withdrawn. Naruto, who was always so full of life and energy, could start to keep to himself more. He might stop seeking his family's approval and focus on his own path, whether it's through training or making new friends outside of the family.
They could become resentful. They might start to avoid Naruto altogether and refuse any summons. They could also start to act out in the forest, scaring away other animals or causing minor disruptions just to show their displeasure.
He could meet an AU version of Hinata who is more assertive and outgoing. Maybe she's a powerful ninja in her own right and not as shy as in the original story.
Perhaps he's been influenced by someone who gives him bad advice. For example, if someone tells him that natural talent is enough and training is overrated. Also, he could be dealing with some personal problems, like a conflict within his family or among his friends that takes up all his time and mental energy, causing him to neglect training.
He might start to rely on his friends more. For example, Sasuke and Sakura could become his main source of emotional support. He would focus on training with them and sharing his feelings, which in turn helps him to grow stronger and more independent.
Well, Kakashi might start by spending more time with Naruto. He could train Naruto more intensively, like teaching him new jutsu. Maybe he also shares his own experiences to give Naruto some guidance and motivation.