A common theme is the clash of different power systems. For example, when Shinobu crosses over into a world like 'Fullmetal Alchemist', her demon slaying powers contrast with the alchemy in that world.
One popular 'shinobu kocho crossover fanfiction' is the one where she crosses over with the world of 'Harry Potter'. In this fic, Shinobu's skills as a demon slayer are put to the test in the magical world. She might have to face new types of 'demons' in the form of dark wizards.
I'm not entirely sure as there could be many different themes in a Kocho Visual Novel. It might be about the adventures of a character named Kocho, or it could revolve around a fictional world with its own set of rules and stories.
Perhaps it has unique art styles. Visual novels often have distinct visuals, so Kocho Visual Novel might stand out with its own kind of character designs or background scenery.
Inosuke doesn't become a Hashira in the manga. The story progresses with him having other significant experiences and achievements instead of achieving that specific position.
It's hard to give an exact number. Different story arcs and battles led to the deaths of multiple hashira. Some died heroically, while others met their fate in unexpected ways. The count changes as the manga progresses.