18+ Sengoku!? - Yuukyuu Ransei Renge Tan

In a world that is a strange combination of the Sengoku Era and modern day, the princess Shizuka has chosen to protect her hometown by becoming a hostage at a more wealthy castle. Despite occasional bouts of loneliness, Shizuka is determined to enjoy herself in her large new town. This mostly involves hanging out with Chouya, the heir to the family of the castle where she now lives. Chouya has a bit of a crush on Shizuka, but how can he flirt with her when one of her favorite pastimes seems to be dressing him up in women's clothing?

(Source: MangaHelpers)