Making a whole thread for a one shot manga seems a bit much, but a single giant thread should do nicely. It will also serve so we can update each other on interesting one shots we've recently found and read.

Souten no Koumori


Alternative Title: A Bat in Blue Sky

Author: Arakawa Hiromu
Serialization: Shounen Gangan
Genres: Action, Historical, Martial Arts, Shounen

Synopsis: Souten no Koumori is a oneshot by the mangaka of Fullmetal Alchemist. It is the story of a shinobi, Henpukumaru, who awakens in an enemy's mansion. She is introduced to the future master of the mansion, Chiyozuru. Chiyozuru is able to get the unemotional Henpukumaru to smile and react differently than she normally would. But, one night, there is an attack by Henpukumaru's former allies...

Resources: ANN | Mangaupdates | MyAnimeList

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From the author of FMA, i felt it was a well told redemption story with great art and actions scenes.

Illuminati Manga - BakaBT