Teisou Gyakuten Sekai no Doutei Henkyou Ryoushu Kishi

Reborn from modern Japan into a medieval fantasy world where gender roles are flipped, Faust is an anomaly—a rare male knight! Raised as a frontier lord, his old-world values clash hilariously with his new life. The queen’s attire leaves little to the imagination, and the busty duke’s “friendly” advances verge on harassment! Despite getting flustered in court, Faust is a dazzling hero on the battlefield whose prowess can turn the tide of any battle.

(Source: Seven Seas Enterainment)