Musashibo Sugaki was a legendary character. He was a monk soldier at the end of the Heian era and one of the traditional representatives of the Japanese Bushido spirit. However, the search results did not mention any specific information about the Musashi Bou tattoo. Therefore, according to the information provided, I don't know the details of Musashi Bou's tattoo.
Since I don't know this particular story, it might be a story that is specific to a certain community or area. It could be about a relationship between a Kabuliwala (someone from Kabul perhaps) and a Bengali woman. But without more information, it's hard to tell the full story.
Another theme is friendship or partnership. Many fanfictions focus on how vault boy and vault girl work together. They rely on each other's skills and strengths. In some stories, their relationship evolves from simple comradeship to a deeper, more meaningful bond over time.
I'm sorry, I'm not familiar with the specific 'kabuliwalar bengali bou' story. It might be a relatively unknown or regional story. You could try to find it in local libraries, ask local storytellers or search in specialized Bengali literature resources.
Unfortunately, without more context, it's difficult to provide the full story of 'bou kotha kou'. It could be a name of a story within a small community or an emerging piece of literature. If you could give some more details like where you heard it from or what kind of story it is (e.g. a love story, a mystery) it would be easier to answer.