It might be a building that houses his own ninja team. Naruto would want a place where his team could relax, plan missions, and store their ninja gear. It could have comfortable living quarters, a library full of mission reports and ninja knowledge, and a large common area for team discussions.
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.
There could also be external threats. Maybe other villains or rival ninja clans see the apartment building as a target. They might try to take it over or destroy it to undermine Naruto's influence in the village. Naruto would then have to use his combat skills and strategic thinking to protect his property.
In the fanfiction, he might own a building that is actually a magical library. Since Harry has always been interested in knowledge, this building could be full of rare and ancient magic books. It could also be a place where wizards and witches from all over come to study and research, and Harry, as the owner, would be in charge of protecting these precious knowledge resources.
He could transform the building into a ninja academy annex. Naruto loves teaching and passing on his knowledge. In this annex, he could offer advanced ninja training, focusing on things he has learned from his own experiences, like dealing with powerful enemies and using the power of friendship and determination.
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.
One possible storyline could be Naruto renovating the apartment building to make it a better place for the villagers to live. He might use his ninja skills to do some unique construction work.
He could turn it into a training ground for young wizards and witches. Teach them how to defend themselves against the dark arts, just like how he was taught at Hogwarts.
Mu Ji Tian Chu was the plaque of Xuanhua Gongji Pavilion.
The cartoon building with eyes might have a curious expression, as if it's constantly observing its surroundings. Maybe it has big, wide-open eyes to show surprise or wonder.
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 sell kunai. Kunai are basic and very popular weapons in the Naruto universe. They are small, easy to handle and can be used in various combat situations.