If you're looking for manga similar to Kei no Seishun, you might like these titles.
Set in the Edo period of Japan, the high-ranking daimyo of the Mito-domain cannot keep his bodyguards alive as they travel Japan. To replenish his bodyguards, they institute a recruitment exam aimed towards the poorest of samurais of Japan, "rounin." As a rounin, Inouse Shinnosuke attempts to prove himself to the ranking officials and escape poverty.
Mounted warriors line up and rush to the assault. Brandishing swords on horseback, the warriors slash at each other... This kind of image of feudal combat is all a lie. Well, then, how did Samurai really fight? A declaration of war has now been made against the lie of combat that was forged during the Edo period, and continued uncontested to this very day.
The manga follows a man named Kazuryuu. Kazuryuu's mother, who was murdered, left him with a memento of the mystery of the "sculpture of the nine-headed dragon." Kazuryuu becomes a medicine seller and an assassin named "Baiyaku" in order to travel Japan and find out the secret of his birth, his name, and his mother's murder.
In early 19th-century Japan, a down-and-out samurai named Ryudo Konosuke struggles through his hardscrabble life. His dear departed mother’s last hope was for him to live his life as a splendid warrior, but a cruel curse repels and distorts any metal that gets near him. Will he ever be able to wield a sword, much less live the life of an honorable samurai? It is said that a samurai’s spirit rests in their sword—and Konosuke can’t even pick one up thanks to a cruel curse that repels anything made of metal that gets near him. Destitute and hopeless, he decides to end it all. But when a beautiful and mysterious woman saves his life and his soul, it is the beginning of Ryudo’s journey into a strange world of magic that exists a step away from his own.