Maybe he buys a training building so that he can practice his ninja skills without being disturbed. It could have special facilities for his shadow clone jutsu practice.
Maybe he buys an old, mysterious building full of secret passages like a wizarding manor. It could have a hidden attic with ancient spells and a cellar where strange potions were once made.
He might want a place of his own, away from the chaos of Hogwarts and the wizarding world's constant threats. A building could be his private sanctuary where he can relax and practice magic without being bothered.
Well, one possibility could be that Naruto uses his henge technique to disguise himself as a girl in order to buy a bra for a female friend who is too shy or unable to do it herself. He might get into all sorts of comical situations in the store, like not knowing the right size or being confused by all the different styles.
One plot twist could be that the'slave' is actually a powerful enemy in disguise, waiting for the right moment to strike Naruto. Another could be that Naruto discovers the slave has a special power or knowledge that changes his view on slavery and makes him want to free the slave instead. Or maybe the village finds out about Naruto's actions and he has to face the consequences, which could be a major plot twist.
He could be buying it for Sakura. Maybe Sakura is in a situation where she needs a new bra but is too busy with her medical ninja duties to go and buy one. Naruto, being the helpful friend he is, decides to use his henge and get it for her.
Naruto's character change in this 'naruto buys a slave' fanfiction could be quite significant. Firstly, his initial innocence and naivete might be replaced with a sense of power and control. His relationships with his friends could also be strained as they may not approve of his actions. He might become more isolated as he tries to justify his new - found position as a slave - owner. Moreover, his self - image could be shattered as he has to confront the fact that he is engaging in an unethical practice, which could lead to a downward spiral of his character development.
Perhaps it's a community building. Naruto is a very community - oriented person. He could own a building that serves as a place for the villagers to gather, like a community center. There could be a cafeteria, a place for kids to play, and rooms for meetings and celebrations.
In many Naruto fanfictions, Naruto finding the ANBU building can lead to all sorts of interesting plot developments. Maybe he stumbles upon it by accident while on a mission. He could be curious about the secrecy surrounding it and decide to investigate, which might get him into trouble with the ANBU or even the Hokage.
Perhaps Naruto is being chased by some enemies and he accidentally runs into the ANBU building. This could lead to an unexpected alliance. The ANBU, initially suspicious of him, realize that he is not a threat and together they fight off the common enemies. After that, Naruto could start to have a more positive relationship with the ANBU, which is a big change from how they were before in the fanfiction.