Hi!

I promised to make a brief summary of the Red Whales and here it is! :) As a source I used volumes 21-24 & 28.

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The Red Whales is kinds of military organization based in Tosa area in Shikoku. Nowadays this area is known as Kouchi prefecture. They have forts all over the Tosa area, but the headquarters is in Urado. In the novel, the members of the Red Whales speak very strong Tosa dialect. 

In their original life they were retainers of Chousokabe clan who ruled the Tosa area in Sengoku era. Their social status was ichiryou gosoku: peasant-warriors. Due to the unfortunate death during the revolt of Urado, most of them became onryou. After being resurrected Kusama and Reijirou founded the Red Whales. Their mission is to make Chousokabe clan great again and protect Tosa from the other clans like Oda and Ichijou. No matter what kind of history, background or religion one has, everyone is welcomed to be a member as long as your heart is connected to the Red Whales.

All original members are hyouireis (=onryous/vengeful spirits). Hyouirei is a soul that possesses someone's body. For example, in the beginning of MoB, Takeda Shingen took over Yuzuru's body and controlled it while Yuzuru's soul was "sleeping". Their difference to kanshousha (Takaya, Naoe) is that kanshousha owns the body he's having, but hyouirei "borrows" it.

And why Takaya is with the Red Whales? He became friend with Ushio after meeting him in the wilderness of Iwa valley. Ushio was struggling with Kusama, Reijirou and Eikichi who wanted him to join them. They wanted him to a member of the Red Whales because Ushio has significant powers that may help them on their mission. Ushio promises to join if Takaya also joins and that's how Takaya started hang with the Red Whales. Reijirou gets very interested in Takaya's skills for killing people just by looking at them, and starts to train him like Ushio is getting trained by Eikichi. Even with this poisonous body Takaya was accepted to be a member, he starts feel the Red Whales as "his family" and decides to stay with them.   

However, a guy called Yoshimura (who doesn't like Takaya at all) sees Takaya speaking with Yasuda Nagahide who exorcised Chousokabe Nobuchika and hears Nagahide calling Takaya 'Kagetora'. He gossips about this to Kusama who is grieving deeply the loss of Nobuchika. Kusama imprisons Takaya and tortures him in many cruel ways. Meanwhile Naoe sneaks into the Red Whales (the fort led by Eikichi) and tries to get know the location of Takaya. He hears rumors that commander Ougi is imprisoned due to the serious matters. While trying to go save Takaya, Naoe gets arrested because Eikichi has realised his true identity. In order to save Takaya, Naoe lies to an assassin of Uesugi and that his mission is to kill traitor Uesugi Kagetora. This lie actually saves Takaya's life since Reijirou's spy, Maki, tells about this to Reijirou who starts to be against for executing Takaya (Kusama is planning to execute him soon). Reijirou, Hayato and Nakagawa don't accept execution but Kusama doesn't listen to them. Few hours before execution Nakagawa sneaks into the jail where Takaya is kept and helps him to escape. While trying to get out they're stopped by Kusama who decides to kill Takaya right away. However, just before Kusama shoots Takaya, Reijirou comes and shoots Kusama injuring him badly. After this Kusama gives up the leadership to Reijirou and Takaya is released.  

Hyouireis:

Kusama Seibee

Brown hair and piercings. Kusama is the leader of the Red Whales. His dream is to revive the great times of Tosa when their lord Chousokabe Motochika ruled the area. In the past Motochika passed away without any grudge so he won't be resurrected anymore. However, his son Nobuchika died with regrets and it's ready for resurrection in Yami Sengoku. Things doesn't go well and Yasuda Nagahide exorcises Nobuchika. After hearing that Nobuchika's killer was Uesugi's spy Kusama starts to feel extremely strong grudge towards to Uesugi. He hears from Yoshimura that Takaya is actually Uesugi Kagetora. Kusama wants his revenge, so he imprisons and tortures Takaya in many horrible ways. However, Reijirou (and the others too) rebels against to him so that he needs to give up his position to Reijirou. Kusama loses his life in vol. 28 due to the huge explosion when Shadow Shikoku is created. 

Kada Reijirou

He is Kusama's close friend and the vice leader of the Red Whales. His host body has black hair with short ponytail. He wants to use retsumyousei for making the Red Whales to be the most powerful one in Yami Sengoku. And he wants humankind to know that the death of physical body isn't the end of life. They have very strong friendship together with Takaya and no wonder he was the most shocked after they got known that Takaya is actually Uesugi Kagetora. When Kusama is about to execute Takaya, Reijirou comes and shoots Kusama. After that Reijirou becomes the leader of the Red Whales.

Hyoudou Hayato

He is the commander of Muroto navy of the Red Whales. He may seem to have very cold personality but he's loyal and trustworthy. He was the only one who reacted in positive way after Takaya's true identity was revealed, because he admires strong persons. Hayato not only respect Takaya but also has feelings for him. He hates Naoe and tries to get of him every time it's possible. He has black hair, his skin is tanned he's almost as tall as Naoe. Usually he wears black leather trousers and black tank top or t-shirt. He loves his rifle that he usually carries with him. No need to say that he is also master at shooting. He manages to become kanshousha after Shadow Shikoku is created.

Nakagawa Kamon

Nakagawa is a gentle and kind doctor. The body he is possessing belonged to a man who wanted make a suicide but let Nakagawa's soul to possess him. He looks a bit like Yuzuru. Nakagawa is doing research for curing Takaya from Kihachi's poison. In his original life his sister was executed by her in-laws without any special reason. Nakagawa went to have his revenge for his sister's unfair death, but lost his life in the battle and that's the reason he became onryou.  

Maki

Maki is Reijirou's right hand and the chief of spying section.

Iwata Eikichi

He's training Ushio. He's quite short and looks a bit like a monkey. Eikichi is an easygoing guy and makes many funny jokes.

Higaki Gokenta

He is the commander of Ashizura navy. He has very short hair and he is very muscular. 

Neiha

The commander of Oki no Shima navy called the White Sharks. They work under the Red Whales but all members are female. She has short hair.

Aotsuki

She's Neiha's right hand. Long curly hair.

Kubuki

Takaya's subordinate in commando unit. He is also a member of Muroto navy. First he had difficulties to accept Takaya for being their commander, but after all Kubuki starts to respect Takaya.

Doumori Inosuke

Takaya's subordinate in commando unit.

Satta Shinjuurou

Takaya's subordinate in commando unit.

Narasaki

Takaya's subordinate in commando unit.

Ichizou

He was spying for the Red Whales. However, he was tired of warring so he stole money and escaped. After being bored to his free life he decided to take Naoe as his master and help him to find Takaya.

Kanshoushas:

Ougi Takaya/Uesugi Kagetora

After being stained by Kihachi's poison Takaya escaped to Shikoku because the poison kills living beings and he was very afraid of injuring Naoe too. In Shikoku he meets Ushio and becomes very good friend with him. Together they join to the Red Whales. Even if everyone in Red Whales thinks Takaya is just normal human, he becomes high ranking commander thanks to his leadership skills and fighting strategy. Nakagawa helps him to live normally by making him special contact lenses and medicine.

Tachibana Yoshiaki/Naoe Nobutsuna

After reunion with Takaya in vol. 24 Naoe was arrested by the Red Whales again. But thanks to Takaya he was released and taken as a new member who is also normal human (not Uesugi's spy) like Takaya. Only leader of the Red Whales know his true identity but to others he's Tachibana.  

Mutou Ushio/Aki Kunitora

Ushio is a guy of his twenties who loves photography and camping. He and Takaya became very close friends and eventually they joined to the Red Whales together. Ushio suffered from memory lost but after being together with Red Whales he started to see dreams about his past life. After all he gets his memories back. His true identity is Aki Kunitora, the lord of Aki area in Shikoku. Chousokabe clan was Aki clan's main enemy and Kunitora was actually killed by the Red Whales.He is also kanshousha like Takaya and can shoot water from his fingertips. 

Nezu Kouichi/Katou Kiyomasa

In his original life, Kiyomasa, the lord of Higo in Kyuushuu, was a very loyal retainer of Toyotomi Hideyoshi. After Yami Sengoku started he worked for Nobunaga but changed his mind after his beloved Kumamoto city was devastated. He joined to the Red Whales just for fun. Kiyomasa uses his own helicopter and he became very loyal ally to Reijirou.