Takasugi Ichirouta is a high school student who is a huge fan of the Warring States period and has been called by his peers a "history otaku". As he was strolling around the ruins of a castle in the north of Gunma prefecture, he suddenly found himself engulfed by a mysterious light. When he came to, he was in the Warring States period! In addition, he ended up in a small castle called Kuoyama Castle which is currently under siege by Houjou's army and has no choice but to get involved in the battle. Will he be able to lead the samurai to defend the castle, all while solving mysteries and being surrounded by beautiful girls? And more importantly, will he be able to go back to his own time period?