Strongest Survival by Otome Game’s Heroine (LN) - Vol 3 Chapter 15: Intruder

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

In the year 2220, a radiation source in the Pacific Ocean, tens of thousands of times stronger than a nuclear bomb has begun mutating exposed creatures into horrific monsters thousands of meters long. Mankind’s only hope was nuclear weapons, which only made matters worse. The combination of the natural radiation and nuclear radiation released an incurable and highly infectious virus, turning the 90% of the world’s population into violent zombies in mere weeks.

This novel is also known as The Demons Beside Me

Chen Zhao can summon demons and see Death.

“Beelzebub, use your Gluttony ability to treat this patient’s anorexia.”

“Raymond, this old man wants to regain his manly function. You know what I mean.”

- Description from Novelupdates

Step inside if you dare, but be warned—this is no ordinary shop. Those who enter never leave the same… if they leave at all. A sinister force lurks within, fueled by a dark past and a thirst for revenge. The price? Twelve lives for twelve sins. As officials race to put an end to the bloodshed, the shop’s deadly grip tightens, claiming innocent victims one by one. Will anyone uncover the truth before it's too late? If you crave spine-tingling horror, heart-pounding thrills, and a mystery that refuses to stay buried, this book will haunt you long after the last page.