Mizu Zokusei no Mahou Tsukai

Ryou finds himself reborn in the world of Phi, expecting a peaceful existence mastering water magic. Instead, he faces harsh wilderness and dangerous creatures on a distant subcontinent. Despite the constant threats, his optimism, intelligence, and the "Eternal Youth" ability allow him to endure. Over twenty years, he steadily grows stronger, approaching the peak of magical power. An unexpected encounter soon places him at the center of major events, altering his path. As he continues to develop his skills, Ryou remains unbothered by urgency, forging his own way toward becoming the most powerful water magician in history.