I Refuse to Save Any Yandere

[Yandere] + [Cthulhu] + [System] (Note: Not everyone is a yandere. Some characters are normal, and having a System doesn't make the protagonist invincible.) (Heartbreak ahead, proceed with caution.) The male lead's soul transmigrates to another world. Here, tentacled monsters serve as the city's arbiters, and magic isn't about throwing fireballs and ice spears at each other. It's about cursing someone to rot to death tomorrow. All the male lead wants in this bizarre world is to survive. But while saving one city after another, he also saves a yandere...