Once there was a military power called "Amamikado" which invaded other countries and expanded its domain.
There were two princes in Amamikado.
The younger prince was named Oguna. His father, the Emperor of Amamikado, trained him as an assassin. Oguna was hungry for power to help his father. This is a tale of an assassin before he meets Izumo.
(Paraphrased from the cover).

Tengen Toppa Gurren Lagann: Gurren Gakuen-Hen (Gurren School Edition) manga that re-imagines cast of TTGL Robot Mecha in a parallel world, at a high school. The people are the same, situations are a bit different with more Ecchi-ness and fanservice for male and female readers. This more or less pokes fun at not only the Anime in general, but also many school based Mangas.

Once there was a legend of a sword. It is said that the sword of a rune god was sealed up in "Jagara-Mogara". When the spirits of Light, Water and Earth come together, the seal will break, then the sword will be immortalised. That is the sword of Susanoh.
Izumo, Kumaso and Oguna, upon pursuing the sword of Susanoh came to the nation of Jagara ruled by an Empress and her army of women. They got involved in the wars between Jagara and Amamikado, but what awaits them isn't the clash between two nations, but the darkness involved with the sword of Susanoh that everyone is seeking.
Credit: Snow Kiss

Tanlou is one of the roaming Blair tribe: a stubborn lot who keep to themselves and frown upon interaction with "outsiders". He, along with six of his friends find a young princess from a nearby castle, wandering in the forest. She begs them to help her, but their help comes with a price. Tanlou is cursed by the head of his clan, and the seven men are banished. Still, they feel compelled to help her. The princess' name? Snow White. After a vicious battle to regain Snow White's kingdom that leaves the princess gravely injured, the evil queen unleashes her wrath, and the unthinkable comes to pass when two of the seven mysteriously disappear, leaving behind five bereft buddies who have no idea what has become of their comrades.
And thus begins the plight of Tanlou and his friends...
(Source: Circeus-Scanlations)

The shogunate installed by the Tokugawa is abiding order, the people live in peace and in a relative prosperity.
However, the dark part of the human heart does not cease to arouse their cupidity: it is the ideal doorway for all demons that, by possessing humans, seek to pass into their world.
Exorcising these demons is Jonosuke's mission, the master of keys. Known for being the best locksmith of Edo, Jonosuke uses particular locks to put the wicked spirits under lock and key. With the help of the bewitching O-kin, a divine who uses unorthodox methods, Jonosuke is going to meet during his demon hunt some notables of his time which will prove to be precious allies when he'll have to face a plot aimed at the upper spheres of the state.
(Source: MU)