The drug powder which Saitou tried to sell to Sanosuke in the guise of Fujita Gorou is the Ishida Sanyaku, a formula which had been in Hijikata's family for generations. It was used frequently in the Shinsengumi for battle wounds and broken bones. In fact, when Hijikata was a child, also son of a farmer (about 11 years old), he was something like Sanosuke, fighting and brawling all day. Then his elder sister married into a household of decent name, and his brother-in-law arranged for him to become a door-to-door medicine seller, selling the Ishida Sanyaku. It was then that he met young Kondou.
Hijikata was feared by many for his mercilessness. Nicknamed "The Demon of Shinsengumi". Can't find the JP name of his katana, though it's of length 2'8". Master strategist and tactician who stretched the prowess of the Shinsengumi to its maximum.
One of the Shinsengumi iron rules was that any traitors, including deserters, had only one path to take: COMMIT SEPPUKU. Yamanami was one such deserter. (See section on Yamanami for more.) After Yamanami split his bowels, he was decapitated by another member of the Shinsengumi, the whole process overseen by Hijikata. I must stress that Hijikata knew Yamanami ever since their Shieikan days, so feel the guy's cold-bloodedness. However, according to Watsuki, in the historical novel 'Moeyoken' (Burning Sword) by Shiba Ryotarou, Hijikata was acting the way he did because he realised that he *was* a leader and could not afford to be soft, though he *did* bring it to the extreme. In that novel, 'he chose to play the part of a demon in front of everybody and killed those he loved, and cried alone in the dark', to quote from Watsuki in his comments about Aoshi. As a leader, he had to be firm and set a good example for his followers irregardless of what he actually felt. I'm sure he's hurting beneath his seemingly cold-blooded facade, after all, they were childhood friends. Perhaps Aoshi keeps his own feelings to himself for the same reason? After all, Hijikata *was* the character model for Aoshi! :)
After the group's defeat in the Boshin War and the death of Kondou, he joined Enomoto Takeaki (a former Bakufu Navy official), escaped to Hokkaido and proceeded to build a so-called "Hokkaido Republic" in order to continue fighting the Ishin government. However, Hijikata was shot to death in a battle in 1869, 2nd Year of Meiji, aged 35. Watsuki's favorite historical figure. And according to many sources including Watsuki, a handsome total knock-out...