Shinnosuke Kagami is the main villain from The Last Blade.
Ever since ancient times, two worlds existed: the world of the living and the world of the dead. These two worlds were separated by Hell's Gate, which kept the balance of the two worlds. The gate was defended by four mighty gods: Seiryu, the white dragon of the east, Byakko, the tiger of the west, Genbu, the tortoise of the south, and Suzaku, the vermilion bird of the north. These four gods watched over the gate from the shadows of history and were forgotten eventually. Legend says that would come the time of the Majin Revival: a time when the four gods would walk the world amongst the mortals and deliver their judgment over them.
During the age known as the Bakumatsu, the end of the Tokugawa Shogunate, Japan starts opening to the foreigners. Unbeknownst to people, the Majin Revival had already come. Suzaku, incarnated in the man known as Shinnosuke Kagami, becomes deeply offended with the mortals, who forgot about their existence and were now accepting foreign ideals, which were outrageous in his vision, as well as forgetting how to live with honor. Kagami decides it's time to unseal Hell's Gate, preparing for the event for five years while mercilessly killing anyone who stood in his way. A master warrior known as Gaisei attempts to stop the maddened Kagami, but he also ends killed. Gaisei is found by his disciple Minataka Moriya, who is mistakenly accused of murdering his master. Knowing nobody would believe him, Moriya takes the blame upon himself and disappears, wanting to avenge his master by himself. The other two disciples of Gaisei, Kaede and Yuki, knew Moriya was not the culprit, deciding to look after their friend and discover who was the real murderer.
Kagami's maddening ends awakening the other three gods: Shigen Naoe, the avatar of Byakko, goes berserk and is imprisoned by Kagami, releasing himself and becoming even more angry; Genbu Okina, an old man and master of Kagami, already aware he was the avatar of Genbu, goes after Kagami and Shigen to calm the two and set things straight; Seiryu was wielded by Kaede himself. However, Kaede didn't wanted to use his divine powers, in fear of losing himself. Many other people are drawn into this chaos, each one by his own reasons, but all connected by a string of fate. Kagami, as to not have any interference on his plan, resurrects the legendary swordsman Musashi Akatsuki, leaving him as he pleased to fight anyone he wanted. Okina manages to call Shigen back to his senses, while Kaede and Yuki finds that Kagami was the one that killed their master. After defeating Moriya, Kaede takes upon himself to stop Kagami. After defeating Musashi, Kaede faces Kagami, finally deciding to use his powers to stop him.
Kagami is defeated by Kaede. Humiliated, he throws himself into Hell's Gate to punish himself for failing his duty. However, the gate is not closed, as the Yellow Dragon, the embodiment of death, escapes the gate and possesses the dead body of Gaisei, becoming known as Kouryu and reopening the portal. Kagami is reincarnated, and now realizing the true potential of mortals decides to take back his role and protect the gate. After Kaede defeats Kouryu, the four gods unite themselves to begin the sealing rite. Yuki, who was the Sealing Maiden, gives up on her life to complete the ritual, as Gaisei uses the power of the four gods to seal the gate forever.
Kagami is a very calm and confident person. During his madness, he becomes arrogant and selfish.