Hair Colour: Bark-Brown
Eye Colour: Hazel
Japanese Seiyu: Tobita Nobuo
English Seiyu: David Matranga
The Secretary-General of the Shinsengumi and a samurai from the Sendai domain.
Sannan Keisuke is a scholarly-looking man with big round glasses. He has dark brown, shoulder length hair that is slicked-back, leaving one lock of bangs on the left-hand side of his face. Sannan wears a casual dark green kimono shirt with a dark blue vest overtop and black open-end pants. In some versions of the Shinsengumi story "Sannan" is considered to be a nickname, with "Yamanami" given as the real pronunciation of his surname (山南), but his canonical name in Hakuouki is "Sannan".
Sannan is a soft-spoken man who doesn't like to make trouble for other people. He especially dislikes being pitied• Sannan deeply cherishes his friends and comrades and tries to help in any way he can for the sake of the Shinsengumi. He has great admiration and respect for Hijikata, even though they don't always see eye to eye.
In the first one in the anime to take Ochimizu due to a hand injury that prevented him from fighting, causing him to be depressed. Sannan is a very intelligent individual, and studies the Ochimizu, even attempting to alter the Ochimizu so its side effects wouldn't affect him.
Sannan's character has become extremely dark; he is now obsessed with finding blood and ways to improve Ochimizu. In fact, he even goes so far to ask Chizuru for blood, due to her demon status. Sannan is intrigued and delighted to find out that Koudou has created a Rasetsu that can survive in daylight. His night-time activities of searching for blood in town and the fact that the Rasetsu are wasting their lives away by using their powers causes the Rasetsu Unit to be shut down.
Nearing the end of the second season, Sannan forges an alliance with Koudou to create more Rasetsu and bring rise to the new demon breed. He is confronted by Hijitaka and Heisuke who oppose the idea and Chizuru refused to take control of the Rasetsu, not wanting to revive her clan. Sannan surprised all them by suddenly attacking the Rasetsu instead of Hijitaka. To him, Shinsengumi orders mean more than anything else.
He used his Rasetsu powers even though he knew full well of the consequences. He mentioned to Koudou that the Rasetsu have no future and they cannot live a normal life because no matter how much the Ochimizu was improved, the shortening of one's life span and going crazy at the sight of blood cannot be cured. After killing off all the Rasetsu and having spent whatever remained of his life force, Sannan fades away alongside Heisuke who also suffered the same fate.
It seems that even in the 21st century, Sannan's underlining obesession with Ochimizu is still apparent & being the school nurse often gives him an excuse to use the ochimizu in order to "treat" injured students & staff like Shinpachi, despite Yamazaki's feeble attempts to stop him.
- Sannan grew surprisingly angry at Chizuru when she made his lunch differently from everyone elses, because he didn't want her "pitying an injured man who may clumsily spill his food," but then ate the food with the others when Chizuru told him that she just did it because she cares for him.
- To the dismay of many, Sannan is never seen without his glasses.
- In Heisuke's route, Sannan turns completely evil in his lust for power via the ochimizu, In the anime, he only pretended to be evil in order to deceive the enemy.
- When Sannan takes the ochimizu, that is technically when Sannan would have "died" in real life.
- Since both "Yamanami" & Sannan" are spelled the same way, there is no "wrong" way to say Keisuke's name, In Hakuouki, they simply refer to him as the later.
- Sannan has a theme track in the anime, however it is mostly used for the Oni.