I'm not sure specifically what the'sama sama letter day story' is about as it's not a widely known common story. It could be a very personal or a story from a specific local or cultural context.
Hentai manga typically focuses on adult or explicit content, while bos manga might have a wider range of themes and may not contain such mature elements.
I'm not sure about this specific work. It might be significant in terms of exploring different perspectives on gay relationships within a family or social context.
Typically, in 'black belly bos pet wife novels', the male lead, who is often a boss or in a high - powered position, has a 'black belly' trait. This means he can be devious or scheming in a non - malicious way, especially when it comes to his relationship with his wife. For example, he might play little tricks on her just to see her reaction but always has her best interests at heart.
Love and romance can be a theme as well, although not in all. Some fanfics explore the romantic feelings that might develop between Loona and the reader. This can be a slow - burn kind of romance, where they first get to know each other on a deeper level before any romantic feelings surface.
There is also 'My Black - bellied Husband's Petting'. It tells a story where the male lead is a successful businessman with a 'black belly' personality. He spoils his wife to no end. The plot often involves his clever ways of dealing with problems that come their way while showing his deep love for his wife.
The Kaguya-sama manga is indeed finished. It ended after a successful run, leaving fans with memories of an engaging and enjoyable story. The final chapters tied up loose ends and delivered a conclusive ending.