Tenohira no Yuki

At ancient times Wano consisted of three large islands where lots of countries and warlords waged war. The story begins when Sudoku is invaded by Mino, and all the key Sudoku people are been killed and deprived. One of survivors is princess who is taken to Mino country. Main character is princess younger brother who switches places with her to avenge his country by attacking women of the castle.

[From vndbreview]