It's a story about a girl who acts as an agent of vengeance from hell. She receives requests from people who have been deeply wronged, and she punishes the wrongdoers by sending them to hell.
One highly recommended naki ghoul fanfiction is 'Naki's Redemption' on AO3. It delves deep into Naki's character, exploring his past and his journey towards redemption in a very engaging way.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, including ones related to Tokyo Ghoul, so there's a good chance you'll find naki ghoul fanfiction there.
One idea could be that the reader is a new ghoul in the area and Naki takes it upon himself to show them the ropes. Maybe he teaches them how to hunt without getting caught. Another plot could involve the reader being injured and Naki protecting them from other ghouls who might see them as easy prey. A third plot idea is that the reader has a special ability that Naki discovers and they team up to use it for their survival in the harsh ghoul world.
First, really understand Naki's character. He's tough but has a soft side. So, show his protective nature towards the reader. Let his actions be guided by his loyalty and his need to belong. For the reader, give them clear goals and fears. Maybe they fear being discovered as a ghoul - lover or they have a goal of helping Naki find his place in the ghoul world. Use their interactions to drive the story forward.
Their relationship could develop slowly. At first, it might be awkward as they are strangers in a way. But Naruto's friendly nature could break the ice. He might share stories about his adventures, which would intrigue Hana. Hana, in turn, could show Naruto the traditions of the Inuzuka clan. They would gradually become friends and then, as they see each other's good qualities more often, fall in love.
One possible fanfiction could be about Naruto going on a mission with Tsume and Hana. They might encounter a powerful enemy in the forest. Naruto could use his shadow clone jutsu to distract the foe while Tsume and Hana attack from the sides. This would showcase their teamwork and different fighting styles.