Tensei Maou-sama wa Yuusha ni Katenai!

There was once a demon lord who ruled over a world far away. On the verge of being slain by the hero Ema, the demon lord, in a desperate attempt to survive, used what he believed to be teleportation magic. However, instead of escaping, he was transported to another world—his body mysteriously shrinking in the process. To make matters worse, he had turned into a little girl. Stripped of all his powers and magic, he found himself being chased by men, trapped in an unfamiliar world with no way out. In this dire situation... "...Are you okay?" Out of nowhere, a voice called out to him. It was the very hero who had cornered him, but she too had been transported here—though a year earlier. Now, the demon lord, lost and powerless, had no choice but to rely on the hero for survival. What kind of chaos will unfold as the demon lord, now in the form of a little girl, is taken in by the hero? The hectic life of the transformed demon lord and the hero begins.

【豪華版】転性魔王さまは勇者に勝てない！ [くまのみそふと] | DLsite

異世界の「最強魔王」が「可愛い女の子」に！TSF（性転換）を扱う新ブランド「くまのみそふと」が贈る第一作！裸パッチやショートボイスドラマなどが付いたDL版豪華特典版です！「DLsite 美少女ゲーム」はエロゲー・エロアニメ・アダルトアニメのダウンロードショップ。お気に入りの作品をすぐダウンロードできてすぐ楽しめる！毎日更新しているのであなたが探している作品にきっと出会えます。国内最大級の二次元総合ダウンロードショップ「DLsite」！