Rappi rangai (Ninja girls)

Rappi Rangai, also known as Ninja Girls (乱飛乱外, Rappi Rangai, lit. Flying out of turbulence turbulent ?), is a manga by Tanaka Hosana. The story takes place during the Sengoku era in Japan and revolves around a boy named Raizou Katana who is loathed and rejected all his life because of a horn on his forehead. The young orphan lives alone in a small house untill one day he finds an almost dead girl named Kagari and nurses her back to health, It turns out that she's a kunoichi serving the Katana clan and was looking for Raizou, who is her recently deceased lord's illegitimate child. Soon they find two of Kagari's fellow kunoichi, Kisarabi and Himemaru who are also devoted to restoring his family name and begine a quest to rebuild the Katana clan.

Trivia

 * There is also a wiki for this manga:

http://rappirangai.wikia.com/wiki/Rappi_rangai_Wiki