Ame no Hi no Iris - Chapter 3 - Execution - battery=03:45:32

“The fallen, the near extinction, those who wish to die, the rich, those who have been loved by life, and those who have been chosen. Are you ready to leave everything you have behind? Are you, the ones chosen by the gods themselves, ready to write history?”“Are you, the reason for the creation of the line between life and death, ready to become holy beings? Are you ready to climb beside Zeus, Odin, Archangel Michael, Lucifer the Fallen Angel, Buddha and others? Are you ready to become a God?”“You've been chosen!” These words would be the words James would hear the most from the moment he entered the tower.Behind the strange events, special feelings and dozens of things lost, James would have only one thing on his mind:“I will break through the tower and meet Chaos himself.”

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

agreed. He thought they might just talk, have a few drinks, and that nothing significant would happen. However, she invited him to a hotel, and they spent the night together.The next morning, she told him it was just a one-night stand and that they would probably never meet again. She said goodbye and left. Ronan also decided to treat it like that.The next day, at his college's hosting club, Ronan was given the responsibility of hosting that year's annual function, where they had invited a singer.When Ronan looked up at the singer, he was shocked—it was the same woman he had spent the night with. After checking her history and social media, he formed an impression of her. Every picture she posted was in revealing clothes, bikinis, or almost nude outfits.He concluded that she was just a promiscuous woman, likely driven by lust, and that she had probably chosen to spend the night with him simply because she found him handsome.Understanding this, Ronan decided to focus on his work. That morning, she had made it clear that it was just a one-night stand and nothing more. He would treat it exactly that way and carry out his responsibilities.Protagonist has System---No NTRIt's Harem, with many girls but The Singer is Main Heroine.