The world was devastated after Great war. All kinds of plants became very rare and there are giants humanoid machines wandering through wastelands. Sahara is a mysterious samurai wielding flower sword who travels to find place which will be able to return the world back to how it was.

Sousuke is the class president, and is a stickler for the rules. Lately, he's had lots of problems. First of all, he's got to deal with his cute, but unruly, childhood friend Miroku. Secondly, they have a new transfer student, Enma, who claims to be from hell. Enma refuses to follow any rules but his own. Lastly, there's the giant, mysterious claw marks that have been appearing all over school buildings. With all this trouble going on, will Sousuke follow the rules or learn that sometimes there are more important things?

From MangaHelpers:
The two boys Gin and Jinrou form a tough team in the mountains. One day, Gin decides that the only way they can move forward is to travel to the capital and join the Shinsengumi.
It soon becomes clear, though, that they are not tough enough to handle the kind of people they find in the capital. Some of them, including the current Shinsengumi members, smell like beasts to Jinrou, and they seem to have unusual abilities. After Gin's tragic death, Jinrou is determined to become stronger and join the Shinsengumi in his place.