I liked this story while the prequel to this "Tamago no Hi" is not really my cup of tea. And since sensei wrote it herself that if was reprinted I reckon this is the older art style of her's. It reminds me a bit of the "Fake" manga. I mean the eyes of the royal brothers, the heavy lided droopy eyes of the Zwei brother, are kind of similar. ╮( ̄▽ ̄)╭
It is so not shoujo! For a moment there I thought it is hentai (bleh), but the much emphasised large breasted-ninja girl was not raped. I would call it ecchi, maybe action(?), calling it historical is asking too much.