Yamakawa Hiroshi’s Kyoto Shugoshoku Shimatsu (京都守護職始末), a history of the office of the protector of Kyoto (Kyoto shugoshoku), was published in 1911.
The office of the protector of Kyoto, which lasted for more than five years, was held by Matsudaira Katamori, daimyo of Aizu. As the protector of Kyoto, he was the master of the Shinsengumi. Yamakawa was a minister to Katamori.
I am very happy that this invaluable source has been republished, in two volumes, complete with annotations, by Heibonsha, a wonderful publisher of books on Japanese history.