It could have been given by the whole village. As a sign of Naruto finally being accepted and respected, the villagers pool their resources to get him a car. This would be a great way to show how far Naruto has come in terms of being recognized as a hero in the village.
Iruka sensei could have given it to him. As Naruto's first teacher and someone who has always supported him, it would be a great way to show his pride in Naruto's growth as a ninja.
Maybe Jiraiya. Since Jiraiya was like a father figure to Naruto, he might have given Naruto a car as a way to help him get around more easily on his adventures and also as a symbol of his trust in Naruto's maturity.
It could be a powerful and mysterious shinobi. Maybe someone from an ancient hidden village who has been observing Naruto for a long time and decided to give him the mask as a test or a way to unlock his true potential.
In fanfiction, the 'kami' could be an original deity created by the author. This new 'kami' could have its own motives and reasons for giving a gift to Naruto. Maybe it's a kami that has been observing Naruto's journey and decides to interfere to help him achieve a greater purpose. It could be a kami associated with nature, like a kami of the wind or the fire, and the gift could be related to that element.
Sasuke would probably be one of the most affected. If Naruto gets a second chance, he might be able to prevent Sasuke from going down the dark path of revenge. Their relationship could develop in a more positive way much earlier.
Aunt May is a very likely candidate. She has always been like a mother figure to Peter. She would notice that he's dirty or injured after a day of being Spider - Man and would gently lead him to the bathroom to get cleaned up. It would be a very nurturing moment between them, with Aunt May scolding him a bit for getting into so much trouble but also showing her love through taking care of him.
It could be a special chakra boost. Since Kyuubi has a vast amount of chakra, it might gift Naruto with an extra dose of chakra that is different from what he already has. This could help Naruto in a difficult battle or in achieving a new jutsu.
Maybe it was Jiraiya. Jiraiya was a very important figure in Naruto's life. He could have given Naruto the mask as part of a training exercise. He might have thought that wearing a mask would force Naruto to rely more on his intelligence rather than his brute strength in certain situations.
It could be an old ninja who has been observing Naruto from afar. This ninja might have seen Naruto's potential and decided to leave the scythe as a test or a way to help him reach his full potential.
In this fanfiction, Naruto might use his second chance to save his friends more effectively. Maybe he could prevent Sasuke from leaving the village earlier by being more understanding of Sasuke's pain and anger. He could also train harder from the start and become even stronger to face the Akatsuki threat more easily.
He could go on rescue missions. For example, if a villager is in trouble in a far - off place, Naruto could quickly drive his car there. His car might be modified with some ninja - like features, like a hidden compartment for his shurikens and kunais.
Maybe a magical amulet. This amulet could have special powers like protecting Naruto from genjutsu or enhancing his chakra control. Since Kami is a powerful entity in the Naruto universe, it makes sense for the gift to have some kind of extraordinary ability.