When it comes to this, I have a lot of ideas for manga. Here are several I can think of, right now:
Shadow Fighter Fumi-18-year old Fumi Hamada, daughter of a gym-owning family, lost her twin sister,Kyoko, at a younger age, only to be haunted by her spirit afterwards. Kyoko can only appear in a inanimated form to be with Fumi since the sisters had a special bond, so she now takes the form of and becomes Fumi's shadow.
Fumi's personal goal is to join the World Class Team Fighting Championships as a master of combat arts such as boxing, kick boxing etc. and Kyoko, who wants her sister to accomplish this dream, assists her by becoming her secret trainer and sparing partner.
Further chars include friends and fighting rivals, some with spiritual accomplices of their own.
Action, and the strong, if not often, competive bond between sisters that even death can not break.
Horror/Supernatural manga focusing on vigilante spirits that take the souls of evil men & women after they scare them to death using their own hidden terrors/phobias.
No Clowning Around(title may be different in time)- Originally from a different dimension populated exclusively by clowns ad various circus folk. a young, scatter-brained harlequin jester turned down his family fortune and heritage, for he has other ideas and that includes being the top funny clown, the highest well-respected expectation.
However, one day he ended up all of a sudden in this dimension.
He freeloads in a house or flathouse meets with a teenage girl, that's constantly bugged and threatened by the landlord there. But this girl has an advantage over the greedy landlord and that is that he has a fear of clowns.
So, the villain conspires and attempt all he can and employ to get rid of the little comedian wannabe.
Soon more clowns come: A sour puss butler to the jester and occasional butt of jokes, an ever feeling blue, melodramatic tragic clown that befriends an equally sensitive but happy, kind child actress and a silent sign-language mastering mime with unusual powers who is friends with a psychic.
Originally, the clowns are payed, except the sour puss one, to return the jester back home. But now they're dragged along for the ride as the mischievous but good-hearted harlequin seeks a warped version of his dream: To entertain the people on Earth.
Usatsuki-(Project I wrote a few chapters on) Sci Fi/Fantasy about five anhro rabbits (Lepu, Lagome, Titan, Rini & Kaze) living in earth's moon (like the rabbit in the moon story) that were abducted by astronauts and brought back to earth for experimenting. Individually, each of them has managed to escape and now live with the Kumamoto Family (Father: Professor Daisuke, Grandmother:Ume, eldest son:Mamoru and young daughter:Tamara.).
However danger is no stranger to the rabbits, who are known as Usatsuki, as they face a renegade scientist after their hides, a possible invasion of the Sasoni, a cruel race of ogre-like beings that are hated enemies with Usatsuki and an aging crime boss that wants their blood for the belief that their blood would him immortal.
Lepu and his "family" face many choices-get back home to the moon, stay on earth with the people they've grown accustomed to or join with the royal usatsuki space army to prevent the carnage of the Sasoni.