As I'm not good summarizing stories, here you can have the synopsis from Animesuki's forum:
I read that the novel is similar to "Madan no Ou to Vanadis", though I haven't read it yet. So far I'm enjoying the 1st novel, the battles and the story are very good and the ecchi and comedy parts are not bad either, a pity that this novel isn't translated yet.This is a world of neverending war. A world where witches are shunned and pursued by humans, which is about to be overthrown. One day a man fell. Through the ceiling of a bathhouse -- in front of the "Witch of the Black Forest" Harrigan. "Wh-wh-what are you doing you Itsuki!?" "Breasts! And they're huge!" -- Suddenly a man from another world appeared in the Witch's land which was waiting to be destroyed -- "H-hey, s-stop, t-touching up my breasts like that!" "Big, big, big breasts!" -- the man dressed in a strange outfit has the name "Dragon King" and has lost his memories -- "A ma-man is touching Ane-sama's b-b-!?" "Calm down Yuuki!" -- so "war ability" and "magic" meets and the gears of destiny will start to turn! Here the curtain will be raised on the glamorous dance of unparalleled wars!