I really enjoyed the first 15 or so chapters but damn this is falling off hard. I'm not sure what's stupider, the idiot prince and his competition vs invasion plan, or how she's going to win with the superior power of glorious nippon culture even though this very European-styled magical feudal world already seems to heavily run on extremely Japanese social mores.
Like a lot of series this feels like the author had a great idea and a strong initial arc, but never really planned beyond that until the work was serialized and they suddenly had a schedule to keep (where before they would've spent time planning now they actually have to churn out chapters).