Kimi to Sekai ga Owaru Hi ni

On the day of his proposal, Hibiki Mamiya, a young man, is trapped in a tunnel collapse accident. When he narrowly escapes from the tunnel, the world has completely changed. A dilapidated cityscape, countless bodies, and the "living dead" wandering around the city... Amidst this abnormal situation, Hibiki desperately searches for his lover, but he is nowhere to be found. Will the few survivors survive together in this hopeless situation?

(Source: COMICSMART, translated)