異世界帰りの剣聖は、自分の実力に気がつかない ～SSSランクの隠しクエストを受けて帰ってきたらレベル１のF級探索者になったけど、異世界で鍛え上げた剣術が強すぎて王女やS級英雄たちが俺を放ってくれません～

Known as the “Weakest Explorer,” Akizuki Yuta dives into dungeons day after day for the sake of his sickly younger sister. One day, he meets Aqua, a beautiful fellow explorer, and together they accept a hidden quest. But the quest sends Yuta to another world, where he’s forced to endure brutally ultra–very-hard adventures. After finally completing the quest and returning home, Yuta finds that he has acquired extraordinary swordsmanship beyond human limits…!