One way to find a good 'Naruto and Kaguya romance fanfiction' is to join Naruto - related fan forums. Fans there often share their favorite fanfictions. They can give you some insider tips on which ones are really well - written and explore the relationship between Naruto and Kaguya in an engaging way.
I'm not sure about a specific 'Naruto and Kaguya romance fanfiction' off the top of my head. However, you could also check out Archive of Our Own (AO3). It has a large collection of fanfictions, and you might be able to discover some great stories about their potential romance by using the right search tags.
Well, you can try looking on fanfiction.net. There are often many creative takes on different pairings there. Maybe search for 'Naruto and Kaguya' and sort by the highest rated ones to find some interesting romance fanfictions.