The novel is written by Hiroaki Samura himself, but it is written by Junichi Ohsako, which makes it basically glorified fanfiction.

This is like an alternate timeline of the first few volumes with a new character thrown in, namely the rabid mutant "sword demon" who's killing the Itto-Ryu. Out of familiar characters, the novel has Manji & Rin (duh), Taito, Anotsu, Makie, Shira and the other Mugai-ryu. At the end, several Itto-Ryu teamed up against one guy, which is breaking the Itto-Ryu code but, to be fair, it was a crazed rabid mutant thing. The really bizarre thing for me about the English translation was that there are no real paragraph. Each sentence is its own paragraph. Doesn't take too long to get used to that, and it makes for a fast, fun read though it lacks the depth of any story arc in the manga.