In Jun Aiba's world, the future is extremely painful and life is meaningless. He made a deal with the God of Death and exchanged his lifespan in three years for a silver watch that could go back in time. This was the twelfth time Ichinose Tsukimi wanted to give up her life, and it was also the twelfth time Aiba Jun saved her. She couldn't figure out why he always came to hinder her plans, and he couldn't understand why someone could be so desperate for life. He went back in time again and again to help her regain hope for the future. Unexpectedly, he began to become more alive. When both of them were ready to rush to the future, the God of Death's advice suddenly sounded - "Never regret giving up your life..."
There is actually this book