Sekai Sukuiowatta kedo, Kioku Soushitsu no Onnanoko Hirotta

A hero, exhausted after defeating a Demon Lord, encounters a red-haired girl being pursued by an unknown enemy and instantly falls for her. She has no memory of her past, and the motives of those chasing her remain unclear. Determined to uncover the truth, he seeks help from former allies: a cynical sage, a knowledgeable knight-princess, a 1,000-year-old child, and a wealthy necromancer. As they face repeated attacks from assassins, his companions grow curious about the girl's identity. When they finally uncover the person behind the threats, they receive a dire warning: if the hero continues to be infatuated with the girl, the world will collapse. With his strongest allies, he continues to uncover her mysterious past.