The following are character descriptions that I gathered from the anime. Please note that there maybe manga/anime differences, from what I gather the manga is a bit more "heavy" unlike the anime which is fairly light at first until it gets more serious towards the end. The anime is continued in the later release of Kurono-san's "Peace Maker Kurogane", however there are overlaps between "Shinsengumi Imon Peace Maker" (SIPM) which is more introductory and "Peace Maker Kurogane" to the anime release.
Ichimura Tetsunosuke 市村鉄之助
Page of Hijikata
Seiyuu: Kobayashi Yumiko 小林由美子
Ichimura Tetsunosuke is a 15 year old strong-willed boy who had wanted to join the Shinsengumi to avenge his parents who were killed two years before the start of this story. His only living relative is an older brother Tatsunosuke. His nickname is "Tetsu" and is usually mistaken for a very young kid, certainly not 15! Indeed this was a problem for him when he first signed up but through the help of Okita Souji he eventually becomes part of the Shinsengumi. His love interest is Saya a young mute girl in Shimabara. Tetsunosuke's journey as Hijikata's page is a long and hard road, couple with the fact that the young man early on in the series has misguided notions of whom and what he fights for.
Simply put I love Tetsunosuke. As a fan of the Shinsengumi, I am awed by his "Shinsengumi wannabee" conviction. He is perhaps your typical boy who wants revenge but in the end, the young boy grows up and matures, able to clearly define what his purpose is through the help of his friends and experiences as a Shinsengumi member.
Name: Ichimura Tatsunosuke 市村辰之助
Accountant under Yamanami
Seiyuu: Ueda Yuuji 上田祐司
Tatsunosuke is the big brother of Tetsu and joins the Shinsengumi reluctantly to support both of them. Since Tetsu is his the only one left of their family, he feels the burden of how to properly take care of Tetsu. Tatsunosuke is a bit of a worry wort when it comes to his younger brother, so much so that at times he hinders Tetsu's growth into maturity. Although Tatsunosuke is also plagued by the death of their parents, Tatsunosuke is the type to play things safe, to let things be so that he and his brother can live their lives in peace.
Tatsunosuke I think is a sweet guy, however, I also believe that he's kind of a weak man as is constantly shown by his comedic appearances asking for pardon to everyone who Tetsunosuke crosses. He's not the type to take charge unless absolutely necessary.
Kondou Isami 近藤勇
Katana: Kotetsu Nagasone
Seiyuu: Hashi Takaya 土師孝也
Kondou Isami is the Commander of the Shinsengumi. He was the head of the Shieikan dojo back in Tama, Edo (Tokyo) and was the master of the Tennen Rishin Ryu. Most of the core members of the Shinsengumi trained under him and followed him from Edo to Tokyo to establish peace in the city. For the most part of the series, he is portrayed as a kind man to most everyone he meets. Unlike his Vice-Commander Hijikata, when there is a chance for relaxation he allows his men to do so. He seems to be a forgiving man, at least to his comrades, but when he is on duty he gets seriously deadly.
Name: Hijikata Toshizo 土方歳三
Oni Fukuchou (Demon Vice-Commander)
Sword: Izumi no Kami Kanesada 和泉守兼定
Seiyuu: Nakata Jouji 中田譲治
Known as the "Demon Fukuchou" or Demon Vice-Commander, Hijikata Toshizo lives up to that reputation. He is a strict man who is feared by not only by outsiders, but other Shinsengumi members. He comes across as cold-hearted and easily annoyed. He is very close to Okita Souji and is a good friend of Kondou. Initially he rejects Tetsunosuke's entry into the Shinsengumi but eventually accepts him as his page after he saw Tetsu's determination. There is perhaps a softer to the Demon Fukuchou.
Name: Yamanami Keisuke 山南敬助
Seiyuu: Inoue Norihiro 井上倫宏
Yamanami Keisuke is also a Fukuchou (Vice-Commander) in the Shinsengumi, however he is Hijikata's opposite such that Yamanami is more gentle and soft-spoken. He is very wise but still when it comes to how to run the group, he and Hijikata end up disagreeing frequently. Although Yamanami is a kind person, this same kindness occasionally catches him off guard, making him doubt at some of the things the group has done and is currently doing in Kyoto.
Name: Okita Souji 沖田総司
Ichi-ban-tai Kumichou (First Troop Captain)
Katana: Kikuichimonji 菊一文字
Seiyuu: Saiga Mitsuki 斎賀みつき
Okita Souji is a bit of a lateral person. He is usually kind and loves children, which is probably why he and Tetsu get along so well. Souji is always smiling and usually have Saizo the pig with him as a pet, however under that smile there is a certain sadness about him that came out when at one point he compared himself to Tetsu while having a spat with Hijikata. As a swordsman, he turns into a completely different person. He becomes fierce and without mercy.
As history dictated, Okita is probably one of the more drastic figures in the Shinsengumi. Even in PMK where he is generally shown as a fun and happy young man, there is definitely times where we all think the opposite.
Name: Nagakura Shinpachi 永倉新八
Ni-ban-tai Kumichoi (Second Troop Captain)
Katana: Ujishige 氏繁
Seiyuu: Yamaguchi Kappei 山口勝平
One of the great comedic trios, Nagakura Shinpachi is a short young man with a bandage on his nose. Usually he is seen hanging around Harada and both of them are usually causing mayhem for Tetsu or just being 'loud' in general. Nagakura likes to brag that he is older amongst the other captains and that he is a good swordsman, which is true as his skills compares to that of Okita and Saitou.
Name: Saitou Hajime 斎藤一
VA: Matsuyama Takashi 松山鷹志
Position: 3rd Squad Captain
Sword: Kunishige 国重
The third captain of the Shinsengumi claims to be able to see the dead and speak with them. He usually has his mala beads with him and prays for the dead. His sword skills are first rate and usually fights Okita to a draw. He likes to dress in black and is quite a loner. He takes a liking to Tetsunosuke and also shares zaru soba with him. Although his characterization at times might come across as bland, he does get some good action and is occasionally quite funny in his own way.
Name: Toudou Heisuke 藤堂平助
VA: Toriumi Kousuke 鳥海浩輔
Position: 8th Squad Captain
The youngest amongst the Captains, Todou Heisuke is a fun good looking young man. He is good friends with Harada and Nagakura. He's a die-hard for cute young boys especially Tetsunosuke. When he gets back to the Mibu headquarters, he completes the comedic trio!
Name: Harada Sanosuke 原田左之助
VA: Nomura Kenji 乃村健次
Position: 10th Squad Captain
Harada is a big man with a big heart. He'll readily protect those who are in trouble, however he is just as quick as to have fun with them along with Nagakura. He is part of the comedic trio. Unlike the others, his specialty is using the spear. He's also committed seppuku before but survived and likes to show it to everyone proudly.
Name: Yamazaki Susumu 山崎烝
VA: Sakurai Takahiro 櫻井孝宏
Susumu is the main spy for the group. He reports to Hijikata any enemy activities especially the Choshuu clan. His does not seem very happy being a ninja but no one knows this excepts for his sister Ayumu. In Susumu's mind, he treats himself as a samurai. He is aloof and keeps up faces to work effectively. In PMK he is quite young which adds to the complexity of his character. Eventually Susumu develops a good relationship with Tetsu.
Name: Yamazaki Ayu 山崎歩
VA: Nagashima Yuko 永島由子
She is known as "Ayu-nee" to the Shinsengumi members. She seems to be the only woman living with the Shinsengumi at the Mibu headquarters. Her main job is to cook for the group but she is also a kunoichi (lady ninja). She is very a very caring person to everyone especially Susumu who is her brother that she worries about the most.
Name: Saizou サイゾー
VA: Takahashi Mikako 高橋美佳子
Everyone's favorite ill-tempered pig! Although Saizou is a pig, Saiou is one of the most memorable characters in the anime for his rather fiesty personality. He dislikes Tetsunosuke it seems and seems to only be happy when he is being cared for by Okita.
Name: Yoshida Toshimaro 吉田稔麿
VA: Suwabe Junichi 諏訪部順一
Position: Choshu leader
He is one of the Choshuu leaders that is an enemy of the Shinsengumi. A very calm, intelligent but cruel man, he is the one who plans to throw Kyoto into chaos and topple the current government. He is also a dark figure in Tetsunosuke's past. Interestingly enough, the character design of Yoshida Toshimaru is very similar to Hijikata, even their names are similar and some of their personalities.
Name: Suzu Kitamura 北村鈴
VA: Yuka Imai 今井由香
Position: Yoshida's page
Like Tetsunosuke, Suzu is a young man who had someone close to him taken away by violence. In order to avenge this person he decided to become Yoshida's page and by some twist of fate ends up being a friend of Tetsunosuke. Eventhough this boy is Choshuu, he is one of my favorite characters in PMK.
Name: Sakamoto Ryoma 坂本竜馬
VA: Ebara Masashi 江原正士
Position: Tosa member
Sakamoto Ryoma is a gun handling man from Tosa who does not seem to be in alliance with either Choshuu nor the Shinsengumi, although he is a wanted man by the Shinsengumi. He bears an uncanny resemblance to Tetsunosuke's father which is why Tetsunosuke is so taken by him.
Name: Saya 沙夜
VA: Takahashi Mikako 高橋美佳子
Position: Geisha in training (Maiko?)
Saya is a mute young girl who is undergoing Geisha training in Shimabara under Akesato. She is a very sweet girl who is Tetsunosuke's love interest.
Name: Akesato 明里
VA: Neya Michiko 根谷美智子
Position: Geisha at Shimabara
Akesato is a woman who lives a double life. During the day time, she is a Geisha in Shimabara who is visited frequently by Yamanami but at night she is a kunoichi who goes against the Shinsengumi.